Push button and teaching pendant with the push button

ABSTRACT

A push-button switch and a teaching pendant employing the same are provided. The push-button switch ensures that a push button is capable of switching ON/OFF the switch if one of contacts thereof should fail during an operation of the switch. For achieving this object, a switch case  3  contains two c-contacts  9   a,    9   b  each having a snap action configuration and switching mechanisms  11   a,    11   b  for opening/closing the c-contacts  9   a,    9   b.  When a push button  5  is depressed, the switching mechanisms  11   a,    11   b  simultaneously open/close the c-contacts  9   a,    9   b  for turning ON/OFF a push-button switch  1.

TECHNICAL FIELD

[0001] The present invention relates to a push-button switch adapted toshift from a first OFF state to an ON state according to the increase ofthe amount of depression of a push button and then to shift to a secondOFF state according to further depression of the push button, and alsorelates to a teaching pendant comprising the same.

BACKGROUND ART

[0002] In cases where, for example, a manual operation is performed onnumerically controlled machines such as robots, an operator often entersa dangerous area to carry out his job. In such cases, a teaching pendantwith a push-button switch, such as called an enable switch (or deadmanswitch), is used for preventing an accident due to contact with themachine during the work.

[0003] As shown in FIG. 34, a teaching pendant 600 is a portable unitwhich is used as connected with a control unit to teach a program to therobot or to operate the robot. The teaching pendant 600 includes aninput keyboard 601 disposed on a main surface and a push-button switch(enable switch) 602 disposed on one side surface thereof. In some cases,the push-button switch 602 may be disposed on a rear surface of theteaching pendant 600. The teaching pendant 600 further includes a signalcable 603 for connection with the control unit not shown.

[0004] Such a teaching pendant employs a push-button switch which iscalled a snap action type, as shown in FIG. 35 for example.

[0005] As seen in FIG. 35, the push-button switch 602 includes a pushbutton 605 and a microswitch 606 in opposing relation with the pushbutton. The push button 605 is provided with a leaf spring 607 extendeddownwardly from a bottom surface thereof. Disposed on a top surface ofthe microswitch 606 are a resilient push plate 608 and an actuator 609.A bent portion 607a is formed at a tip of the leaf spring 607.

[0006] The push-button switch 602 is used as follows. First, theteaching pendant 600 incorporating the push-button switch 602 isconnected, via the signal cable 603, with a control panel of a machineto be manually operated. If the push-button switch 602 is in the OFFstate at this time, manipulating the keyboard 601 of the teachingpendant 600 does not effect the key entry.

[0007] Next, depressing the push button 605 brings the bent portion 607a of the leaf spring 607, moved in unison with the push button 605, intoengagement with the push plate 608 of the microswitch 606. At the sametime, the push plate 608 is resiliently deformed downward to press downthe actuator 609, as shown in FIG. 36. This causes the actuator 609 todescend to bring a contact within the microswitch 606 into a contactedstate, so that the microswitch 606 is shifted to the ON state.

[0008] The operator performs key entry via the keyboard 601 of theteaching pendant 600 while keeping the push button 605 depressed so asto maintain the microswitch in the ON state. If, during the operation,the operator releases the push button 605 sensing the danger ofcontacting some moving part of the machine manually operated, the pushbutton 605 returns to the state shown in FIG. 35, thereby shifting themicroswitch 606 to the first OFF state or the initial state. That is,the machine is brought into standstill.

[0009] In a case where the operator, who is in panic facing the imminentdanger, further depresses the push button 605, the bent portion 607 a ofthe leaf spring 607 slides on the push plate 608 to disengage therefrom,as shown in FIG. 37, so that the push plate 608 is returned to itsoriginal position by its restoring force. This shifts the microswitch606 to the second OFF state for deactivating the machine.

[0010] Thus, the push-button switch 602 is adapted to permit the keyentry through the keyboard 601 of the teaching pendant 600 only when themicroswitch 606 is in the ON state. Furthermore, the push-button switch602 can be set to any of the three positions (the first OFF state, ONstate and second OFF state) according to the amount of depression of thepush button 605. Therefore, the operator's intent during the manualoperation of the machine can be distinctly implemented and hence, theoperator's safety is ensured.

[0011] As the push-button switch having such three positions, there maybe employed a push-button switch of a so-called slow action type, asshown in FIG. 38.

[0012] As shown in FIG. 38, such a push-button switch 701 includes aswitch case 702, a push button 703 depressibly supported by the switchcase 702, a pair of stationary terminals 705 each attached to a leafspring 704 disposed within the switch case 703, a pair of movableterminals 707 attached to a bracket 706 and adapted to be brought intoor out of contact with the stationary terminals 705, and a switchingmechanism 708 moving in response to the depression of the push button703 for bringing the movable terminals 707 into contact with thestationary terminals 705 and designed to separate the movable terminals707 from the stationary terminals 705 when the depression of the pushbutton reaches a predetermined amount. In the push-button switch 701,the movable terminal 707 and the stationary terminal 705 constitute anormally open contact.

[0013] The push button 703 is formed with an accommodating portion 709defining a rectangular internal space in plan, the accommodating portion709 formed with slopes 710 on opposite walls thereof.

[0014] The switching mechanism 708 includes an insertion member 712disposed in the accommodating portion 709 of the push button 703 andformed with a pair of bores 711, a pair of slide blocks 713 disposed inthe respective bores 711 of the insertion member 712 as allowed to movehorizontally (the transverse direction as seen in FIG. 38), a helicalspring 714 interconnecting the insertion member 712 and the bracket 706and urging the movable terminals 707 downwardly, and a shaft member 715projecting downward from the bracket 706.

[0015] The slide blocks 713 are urged toward opposite ends of the pushbutton 703 by helical springs 716 disposed in the respective bores 711of the insertion member 712. The slide blocks 713 are each formed with aslope 717 at one end thereof for engagement with each of the slopes 710of the push button 703.

[0016] The shaft member 715 has its lower portion inserted in a bore 718formed at a bottom of the switch case 702. Disposed in the bore 718 is areturn spring 719, an upper end of which is fixed to a lower end of theshaft member 715. Thus, the shaft member 715 is normally urged upward byan urging force of the return spring 719.

[0017] When the undepressed push button 703 in the first OFF state isdepressed, the switching mechanism 708 is moved downward as interlockedwith the push button 703 thereby pushing down the movable terminals 707into contact with the stationary terminals 705, as shown in FIG. 39.Thus, the push-button switch 701 is shifted to the ON state. At thistime, the slopes 710 of the push button 703 apply a pressure to theslopes 717 of the slide blocks 713 for moving the slide blocks 713inwardly. However, the urging force of the helical spring 714 urging theslide blocks 713 upwardly is greater than this pressure, so that theslide blocks 713 stay at places to maintain the engagement with the pushbutton 703.

[0018] When the push button 703 in the ON state is further depressed,the urging force of the helical spring 714 surpasses the force forurging the slide blocks 713 outwardly, so that the slide blocks 713 aremoved inwardly of the insertion member 712 as the slopes 717 of theslide blocks 713 slid on the slopes 710 of the push button 703, as shownin FIG. 40. This results in the disengagement of the slide blocks 713from the push button 703, while the switching mechanism 708 is movedupward by the return spring 719, as shown in FIG. 41. This movementinvolves an upward movement of the movable terminals 707, which areseparated from the stationary terminals 705. Thus, the push-buttonswitch 701 is shifted to the second OFF state.

[0019] The above conventional push-button switches 602, 701 are providedwith only one contact. In a case where the contact does not work due tofailure or the like during the data input operation, for example, thepush-button switch is unable to respond to the ON/OFF switching, thuslosing the function as the enable switch. Accordingly, the push-buttonswitch fails to assure reliability.

[0020] In the push-button switch 701 of slow action type, the amount ofdepression of the push button 703 to shift the switch from the first OFFstate to the ON state is equal to the amount of depression of the pushbutton 703 to shift the switch from the ON state to the first OFF state.Therefore, if the depressed push button 703 of the push-button switch701 in the ON state is released a little, for example, the movableterminals 707 move away from the stationary terminals 705. That is, thepush-button switch 701 is prone to return from the ON state to the firstOFF state. In the case of a long data input operation through theteaching pendant, for example, the operator may encounter an inadvertentinterruption of the data input because an unintentional slight easing ofthe depression of the push button will return the push-button switch 701to the first OFF state.

[0021] Furthermore, the push-button switch 701 of slow action type doesnot provide a tactile click-touch or a click sound when the switch isshifted from the first OFF state to the ON state. Hence, it is difficultfor the operator pressing down the push button 703 to determine whetherthe push-button switch 701 is in the ON state or enabled for data entry.

[0022] In view of the foregoing, it is an object of the presentinvention to provide a push-button switch ensuring the ON/OFF switchingthereof despite a failure of one contact during the manipulation of thepush-button switch and to provide a teaching pendant employing the same.

[0023] It is another object of the present invention to provide apush-button switch adapted to prevent an unintentional shifting from theON state to the first OFF state as a result of a slight easing of thedepression of the push button and to provide a teaching pendantemploying the same.

DISCLOSURE OF THE INVENTION

[0024] In accordance with the present invention for achieving the aboveobjects, a push-button switch comprises a switch case; a push buttondepressibly supported by the switch case; a contact comprising a movableterminal disposed in the switch case in a manner that a first endthereof is rotatable about a second end thereof, and a normally openstationary terminal fixed to place in the switch case and arranged to bein or out of contact with the movable terminal through the rotation ofthe first end of the movable terminal; an operative member disposed inthe switch case in a manner that a first end thereof is rotatable asinterlocked with the depression of the push button; urging means havingits opposite ends locked to the first end of the movable terminal andthe first end of the operative member for urging the first end of themovable terminal while urging the first end of the operative member in afirst direction; and releasing means brought into action by more than apredetermined amount of depression of the push button to release theoperative member from the interlocked relation with the push button, andis characterized in that when in conjunction with the increase of theamount of depression of the push button, the amount of rotation of thefirst end of the operative member against the urging means is increasedto a first dead point at which the urging force applied by the urgingmeans to the movable terminal is changed from the first direction to asecond direction, the movable terminal is brought into contact with thenormally open stationary terminal thereby shifting the contact from afirst OFF state to an ON state, that when the amount of rotation of thefirst end of the operative member released from the rotation against theurging means reaches a second dead point at which the urging forceapplied by the urging means to the movable terminal is changed from thesecond direction to the first direction, the movable terminal is movedaway from the normally open stationary terminal thereby shifting thecontact from the ON state to a second OFF state, and that two or more ofthe contacts are disposed in the switch case and are simultaneouslyturned ON or OFF by depressing the push button.

[0025] According to such an arrangement wherein two or more contacts forswitching the push-button switch between the ON and OFF states aredisposed in the switch case, the contacts can simultaneously be turnedON or OFF by depressing a single push button. Therefore, in the case ofa failure of one of the contacts, for example, the push-button switchcan be switched between the ON and OFF states by means of the othercontacts. Thus, the push-button switch is improved in reliability.

[0026] The push-button switch according to the present invention ischaracterized in that as to transition from the ON state to the firstOFF state resulting from eased depression of the push button, the amountof rotation of the first end of the operative member to reach the seconddead point is set smaller than that of rotation of the first end of theoperative member to reach the first dead point.

[0027] According to this arrangement wherein the amount of rotation ofthe first end of the operative member to reach the second dead point isset smaller than that of rotation of the first end thereof to reach thefirst dead point, the movable terminals are separated from the normallyopen stationary terminals by a smaller amount of depression of the pushbutton than that required for bringing the movable terminals intocontact with the normally open stationary terminals.

[0028] That is, the push-button switch has a so-called hysteresischaracteristic that the switch requires a different amount of rotationof the first end of the operative member to be shifted from the firstOFF state to the ON state than that required to be shifted from the ONstate to the first OFF state. Therefore, even if the depression of thepush button for maintaining the push-button switch in the ON state iseased, for example, the movable terminals are not separated from thenormally open stationary terminals so long as the decrease of thedepression of the push button is within a predetermined range or unlessthe amount of rotation of the operative member reaches the second deadpoint. Thus, the push-button switch is prevented from beinginadvertently shifted from the ON state to the first OFF state.

[0029] The push-button switch according to the present invention ischaracterized in that one of the contacts includes a normally closestationary terminal, and that the one contact maintains the movableterminal and the normally close stationary terminal thereof in contactedrelation when the other contacts are in the first OFF state, maintainingthe movable terminal and the normally close stationary terminal thereofin separated relation when the other contacts are in the ON state,maintaining the movable terminal and the normally close stationaryterminal thereof in contacted relation when the other contacts are inthe second OFF state.

[0030] According to this arrangement wherein the one contact assumes theopposite open/close position to that assumed by the other contacts whenthe push-button switch is shifted from the first OFF state to the ONstate or from the ON state to the second OFF state, it is readilydetermined that any one of the contacts is in failure when the onecontact and the other contacts assume the open or close position at atime.

[0031] The push-button switch according to the present invention ischaracterized in that an auxiliary contact is disposed in the switchcase, the auxiliary contact designed to be opened or closed when thecontacts are in the first OFF state and to be closed or opened when thecontacts are in the second OFF state.

[0032] According to this arrangement wherein there is provided theauxiliary contact switched between the open and close positionsdepending upon the first OFF state and the second OFF state, whether thepush-button switch is in the first OFF state or in the second OFF statecan be determined by monitoring the open/close position of the auxiliarycontact.

[0033] More specifically, the movable terminals and the normally openstationary terminals of the contacts are open when the push-buttonswitch is in the first OFF state and when the push-button switch is inthe second OFF state. Therefore, it is impossible to determine thepush-button switch to be in the first OFF state or in the second OFFstate by merely monitoring the open/close relation between the movableterminals and the normally open stationary terminals. However, theprovision of such an auxiliary contact permits the determination as towhether the push-button switch is in the first OFF state or in thesecond OFF state.

[0034] The push-button switch according to the present invention ischaracterized in that the auxiliary contact is provided incorrespondence to each of the contacts. According to this arrangementwherein the auxiliary contact is provided in correspondence to each ofthe contacts, each of the contacts can be determined to be in the firstOFF state or in the second OFF state by monitoring the correspondingauxiliary contact.

[0035] The push-button switch according to the present invention ischaracterized in that the auxiliary contact comprises a normally closecontact designed to be closed when the contacts are in the first OFFstate and to be opened when the contacts are in the second OFF state,and is provided with forcible separation means for forcibly opening theauxiliary contact in the second OFF state.

[0036] According to this arrangement, in a case where the auxiliarycontact is fused, for example, the forcible separation means canforcibly open the auxiliary contact. This provides a positivedistinction between the first OFF state and the second OFF state of thepush-button switch.

[0037] The push-button switch according to the present invention furthercomprises a distribution member for evenly distributing a pressing loadapplied by depressing the push button. According to this arrangement,whatever portion of the push button is depressed, the distributionmember evenly distributes the pressing load. This ensures that theplural contacts are opened or closed at a time.

[0038] The push-button switch according to the present invention furthercomprises a rubber cover mounted to place in a manner to cover the pushbutton. According to this arrangement wherein the push button is coveredby the rubber cover, the push-button switch is enhanced inwatertightness.

[0039] The push-button switch according to the present invention furthercomprises an external button mounted to place in a manner to cover thepush button. According to this arrangement wherein the push button iscovered by the external button, a top surface of the push button isprotected against deformation or fracture.

[0040] In accordance with the present invention, a teaching pendant ischaracterized in that a pendant body includes a left-hand and aright-hand operation sections to be held in the left hand and the righthand, respectively, and the push-button switches disposed at therespective inner sides of the operation sections to be operated bygripping the corresponding operation sections, and that gripping eitherone of the operation sections shifts the corresponding push-buttonswitch to the ON state thereby enabling a data input operation.

[0041] According to this arrangement wherein there are provided theleft-hand and right-hand operation sections with the respectivepush-button switches to be operated by gripping the correspondingoperation sections, the data input operation can be done by either hand.In a case where, for example, the left hand is fatigued while depressingthe left-hand operation section in order to maintain the push-buttonswitch in the ON state for data input operation, the pendant body may beheld by the right hand, in turn, so that the push-button switch may bemaintained in the ON state via the right-hand operation section.

[0042] The teaching pendant according to the present invention ischaracterized in that when either one of the operation sections isgripped to shift the corresponding push-button switch at the inner sidethereof to the second OFF state, the gripping of the other operationsection does not enable the operation of the corresponding push-buttonswitch at the inner side thereof.

[0043] According to this arrangement wherein with either one of thepush-button switches placed in the second OFF state, the otherpush-button switch is disabled for operation, an effort to shift theother push-button switch to the ON state, for example, is ineffective toplace the teaching pendant in the teaching mode. Thus, the data inputoperation is inhibited.

[0044] In accordance with the present invention, a teaching pendant ischaracterized in that a pendant body is provided with one piece of thepush-button switch and a right-hand and a left-hand manipulation leversto be gripped by the right hand and left hand, respectively, foroperative depression of the push-button switch, and that either one ofthe manipulation levers is manipulated to shift the push-button switchto the ON state, thereby enabling a data input operation.

[0045] According to this arrangement wherein the left-hand andright-hand manipulation levers are provided and the push-button switchcan be operated via either of the manipulation levers, even when theleft hand involved in the operation is fatigued, for example, thependant body may be held in the right hand so as to continue the datainput operation. Furthermore, the teaching pendant is reduced in costsbecause only one push-button switch is provided in the pendant body.

[0046] The teaching pendant according to the present invention ischaracterized in that when either one of the manipulation levers isgripped to shift the push-button switch to the second OFF state, thegripping of the other manipulation lever does not enable the operationof the push-button switch.

[0047] According to this arrangement, when the push-button switch isshifted to the second OFF state by gripping either one of themanipulation levers, the other manipulation lever is disabled foroperation. Hence, data cannot be inputted unless both of themanipulation m levers are manipulated to shift the push-button switch tothe first OFF state.

BRIEF DESCRIPTION OF THE DRAWINGS

[0048]FIG. 1 is a sectional front view showing one state of apush-button switch according to a first embodiment of the presentinvention;

[0049]FIG. 2 is a sectional front view showing another state of thepush-button switch according to the first embodiment hereof;

[0050]FIG. 3 is a sectional front view showing yet another state of thepush-button switch according to the first embodiment hereof;

[0051]FIG. 4 is a sectional front view showing still another state ofthe push-button switch according to the first embodiment hereof;

[0052]FIG. 5 is a group of sectional views taken on the line A-A in FIG.1;

[0053]FIG. 6 is a graph representing a relation between the amount ofrotation of an operative member of the first embodiment and the pressureload thereon;

[0054]FIG. 7 is a group of circuit connection diagrams according to thefirst embodiment hereof;

[0055]FIG. 8 is a graph representing a relation between the operationstroke and the operating load of a push button according to the firstembodiment hereof;

[0056]FIG. 9 is a group of diagrams showing an exemplary modification ofthe circuit connections according to the first embodiment hereof;

[0057]FIG. 10 is a group of diagrams showing another exemplarymodification of the circuit connections according to the firstembodiment hereof;

[0058]FIG. 11 is a sectional front view showing one state of apush-button switch according to a second embodiment hereof;

[0059]FIG. 12 is a sectional front view showing another state of thepush-button switch according to the second embodiment hereof;

[0060]FIG. 13 is a sectional front view showing yet another state of thepush-button switch according to the second embodiment hereof;

[0061]FIG. 14 is a sectional front view showing one state of apush-button switch according to a third embodiment hereof;

[0062]FIG. 15 is a sectional front view showing another state of thepush-button switch according to the third embodiment hereof;

[0063]FIG. 16 is a sectional front view showing yet another state of thepush-button switch according to the third embodiment hereof;

[0064]FIG. 17 is a sectional front view showing still another state ofthe push-button switch according to the third embodiment hereof;

[0065]FIG. 18 is a sectional front view showing one state of apush-button switch according to a fourth embodiment hereof;

[0066]FIG. 19 is a sectional front view showing another state of thepush-button switch according to the fourth embodiment hereof;

[0067]FIG. 20 is a sectional front view showing yet another state of thepush-button switch according to the fourth embodiment hereof;

[0068]FIG. 21 is a sectional front view showing still another state ofthe push-button switch according to the fourth embodiment hereof;

[0069]FIG. 22 is a sectional front view showing one state of apush-button switch according to a fifth embodiment hereof;

[0070]FIG. 23 is a sectional front view showing another state of thepush-button switch according to the fifth embodiment hereof;

[0071]FIG. 24 is a sectional front view showing yet another state of thepush-button switch according to the fifth embodiment hereof;

[0072]FIG. 25 is a sectional front view showing still another state ofthe push-button switch according to the fifth embodiment hereof;

[0073]FIG. 26 is a front view showing a teaching pendant according to asixth embodiment hereof;

[0074]FIG. 27 is a perspective view of the teaching pendant of the sixthembodiment hereof as seen from the rear side;

[0075]FIG. 28 is a circuit connection diagram for explaining theoperations of the sixth embodiment hereof;

[0076]FIG. 29 is a circuit connection diagram for explaining theoperations of the sixth embodiment hereof;

[0077]FIG. 30 is a circuit connection diagram for explaining theoperations of the sixth embodiment hereof;

[0078]FIG. 31 is a rear view showing a teaching pendant according to aseventh embodiment hereof;

[0079]FIG. 32 is a group of diagrams explanatory of the operations ofthe teaching pendant according to the seventh embodiment hereof;

[0080]FIG. 33 is a diagram showing an exemplary modification of theteaching pendant according to the seventh embodiment hereof;

[0081]FIG. 34 is a perspective view showing a teaching pendantcomprising a conventional push-button switch;

[0082]FIG. 35 is schematic diagram showing an arrangement of theconventional push-button switch;

[0083]FIG. 36 is a diagram explanatory of the operations of theconventional push-button switch;

[0084]FIG. 37 is a diagram explanatory of the operations of theconventional push-button switch;

[0085]FIG. 38 is a sectional front view showing another conventionalpush-button switch;

[0086]FIG. 39 is a sectional front view showing another state of thepush-button switch of FIG. 38;

[0087]FIG. 40 is a sectional front view showing yet another state of thepush-button switch of FIG. 38; and

[0088]FIG. 41 is a sectional front view showing still another state ofthe push-button switch of FIG. 38.

BEST MODES FOR PRACTICING THE INVENTION

[0089] (First Embodiment)

[0090] A first embodiment of the present invention will be describedwith reference to FIGS. 1 to 10. FIGS. 1 to 4 are sectional front viewsshowing different states of a push-button switch; FIG. 5 is a group ofsectional views taken on the line A-A in FIG. 1; FIG. 6 is a graphrepresenting a relation between the amount of rotation of an operativemember and the load thereon; FIGS. 7, 9 and 10 are connection diagramsof the push-button switch according to the first embodiment; and FIG. 8a graph representing a relation between the operation stroke and theoperating load of a push button.

[0091] As shown in FIG. 1, a push-button switch 1 according to thisembodiment comprises a switch case 3 of a rectangular shape in plan; apush button 5 depressibly supported by the switch case 3; a normallyclose contact 7 as an auxiliary contact and two c-contacts 9 a, 9 bdisposed in the switch case 3; and two switching mechanisms 11 a, 11 bdisposed in the push button 5 and adapted to open/close thecorresponding c-contacts 9 a, 9 b as interlocked with the depression ofthe push button 5.

[0092] Within the switch case 3, the normally close contact 7 isdisposed centrally of a lower portion thereof whereas the c-contacts 9a, 9 b are disposed on opposite ends thereof as sandwiching the normallyclose contact 7 therebetween. The switch case 3 is formed with flanges13 a, 13 b on lateral sides of an outside surface thereof. The flanges13 a, 13 b are fixed to a teaching pendant for data entry or the like bymeans of screws or the like.

[0093] The normally close contact 7 comprises a movable member 15located within the switch case 3 and projecting toward the push button 5(upward); a pair of movable terminals 17 a, 17 b each attached to alower end of the movable member 15 via a conductive member 16; and apair of stationary terminals 19 a, 19 b arranged to be in or out ofcontact with the corresponding movable terminals 17 a, 17 b.

[0094] The movable member 15 has a helical spring 21 attached to thelower end thereof, the helical spring 21 urging the movable member 15upwardly. In an initial state wherein the push button 5 is undepressed,the normally close contact 7 is closed with the movable terminals 17 a,17 b kept in contact with the stationary terminals 19 a, 19 b by anurging force of the helical spring 21. Projected from a lower end of theswitch case 3 are two metallic terminal pieces 23 a, 23 b, which areelectrically connected with the stationary terminals 19 a, 19 b of thenormally close contact 7, respectively.

[0095] The c-contacts 9 a, 9 b are disposed under partitioning walls 25a, 25 b of an L-shape in section formed at the opposite ends of theswitch case 3, respectively. The c-contacts 9 a, 9 b each comprise asnap action configuration including a movable terminal 31 a, 31 b, afirst end 27 a, 27 b of which is rotatable about a second end 29 a, 29 bthereof; a normally close stationary terminal 33 a, 33 b and a normallyopen stationary terminal 35 a, 35 b disposed above and below the movableterminal 31 a, 31 b, respectively; an operative member 43 a, 43 b, afirst end 39 a, 39 b of which is rotated about its second end 41 a, 41 bas pressed by a pressing section 37 a, 37 b of the switching mechanism11 a, 11 b to be described hereinafter; and a helical spring 45 a, 45 bwith opposite ends locked to the first end 27 a, 27 b of the movableterminal 31 a, 31 b and to the first end 39 a, 39 b of the operativemember 43 a, 43 b for urging upward the first end 27 a, 27 b of themovable terminal 31 a, 31 b as well as the first end 39 a, 39 b of theoperative member 43 a, 43 b.

[0096] In the initial state wherein the push button 5 is undepressed, asshown in FIG. 1, the push-button switch 1 is in the first OFF statewherein the movable terminals 31 a, 31 b of the c-contacts 9 a, 9 b areurged upward by the helical springs 45 a, 45 b thereby being kept awayfrom the normally open stationary terminals 35 a, 35 b but in contactwith the normally close stationary terminals 33 a, 33 b.

[0097] The movable terminal 31 a, normally close stationary terminal 33a and normally open stationary terminal 35 a of the c-contact 9 a on oneside are electrically connected with terminal pieces 46 a, 47 a, 48 aprojecting from the bottom of the switch case 3, respectively. Likewise,the movable terminal 31 b, normally close stationary terminal 33 b andnormally open stationary terminal 35 b of the other c-contact 9 b on theother side are electrically connected with terminal pieces 46 b, 47 b,48 b projecting from the bottom of the switch case 3, respectively.

[0098] The push button 5 is formed with an accommodating portion 49extending vertically and defining a rectangular space in plan. Theaccommodating portion 49 has a centrally located pressing member 51 fordepressing the normally close contact 7. Disposed on laterally oppositesides of the pressing member 51 are partitioning plates 53 a, 53 b of anL-shaped section each dividing the accommodating portion 49 into anupper portion and a lower portion. The switching mechanisms 11 a, 11 bfor opening/closing the c-contacts 9 a, 9 b are disposed in uppercavities 55 a, 55 b defined by the partitioning plates 53 a, 53 b,respectively.

[0099] The push button 5 is formed with projections 57 a, 57 b projecteddownward from opposite ends thereof. The projections 57 a, 57 b havehelical springs 59 a, 59 b fitted thereover, respectively. Lower ends ofthe helical springs 59 a, 59 b are fixed to opposite ends of the bottomof the switch case 3 so that the push button 5 is normally urged upwardby urging forces of the helical springs 59 a, 59 b.

[0100] The switching mechanisms 11 a, 11 b each comprise the a pressingsection 37 a, 37 b for depressing the operative member 43 a, 43 b of thec-contact 9 a, 9 b; a slide block 61 a, 61 b for pushing down thepressing section 37 a, 37 b as interlocked with the depression of thepush button 5; and a pressing shaft 63 a, 63 b locked to the slide block61 a, 61 b.

[0101] The pressing section 37 a, 37 b extends downward from place in agap 64 a, 64 b defined between the partitioning plate 53 a, 53 b and thepressing member 51 and has its lower end abutted against the first endof the operative member 43 a, 43 b of the c-contact 9 a, 9 b.

[0102] The pressing shaft 63 a, 63 b has a hollow structure and is urgeddownward by a helical spring 65 a, 65 b which is attached to an upperinside wall of the push button 5 and has its lower end fixed to placeinside of the pressing shaft 63 a, 63 b.

[0103] The pressing shaft 63 a, 63 b is inserted through a through hole67 a, 67 b formed in the partitioning plate 53 a, 53 b. On the otherhand, a flange 69 a, 69 b at an upper end of the pressing shaft 63 a, 63b is locked to the partitioning plate 53 a, 53 b at a circumference ofthe through hole 67 a, 67 b so that the pressing shaft 63 a, 63 b isrestrained from moving downwardly (dropping-off). The flange 69 a, 69 bof the pressing shaft 63 a, 63 b is formed with a slope 71 a, 71 b onone lateral side thereof.

[0104] The slide block 61 a, 61 b is formed with a cavity 73 a, 73 bvertically extended therethrough, in which cavity 73 a, 73 b thepressing shaft 63 a, 63 b is inserted. The slide block 61 a, 61 b isdisposed in the upper cavity 55 a, 55 b defined in the accommodatingportion 49 by the partitioning plates 53 a, 53 b, as allowed to movehorizontally (the transverse direction as seen in FIG. 1). A helicalspring 75 a, 75 b is interposed between a first end of the slide block61 a, 61 b and a side surface of the partitioning plate 53 a, 53 b forurging the slide block 61 a, 61 b toward the center of the push button5.

[0105] The slide block 61 a, 61 b is adapted to abut against an upperend of the pressing section 37 a, 37 b at a second end thereof. Thus,the slide block 61 a, 61 b is moved downwardly as interlocked with thedepression of the push button 5, thereby pressing down the pressingsection 37 a, 37 b. Furthermore, the slide block 61 a, 61 b is formedwith a slope 79 a, 79 b on one inside wall thereof defining the cavity73 a, 73 b. The slope 79 a, 79 b is locked to the slope 71 a, 71 b ofthe flange 69 a, 69 b of the pressing shaft 63 a, 63 b.

[0106] As shown in FIGS. 1 and 5, a U-shaped distribution member 81 isdisposed between the partitioning plate 53 a, 53 b and the partitioningwall 25 a, 25 b. The distribution member 81 has its upper end rotatablyretained by a lower surface of the partitioning plate 53 a, 53 b via aretaining member 83 a, 83 b and its lower end 81 a, 81 b retained in acavity 87 a, 87 b defined between an upper surface of the partitioningwall 25 a, 25 b and a guide member 85 a, 85 b disposed thereabove in amanner to be slidably movable in the horizontal direction (theanteroposterior direction as seen in FIG. 1).

[0107] When the push button 5 in the initial state, shown in FIG. 5(a),is depressed, the distribution member 81 rotates about the upper endthereof in the direction of α in FIG. 5(a) with its lower end 81 a, 81 bsliding in the cavity 87 a, 87 b. When the push button is fullydepressed, the distribution member 81 assumes a position as shown inFIG. 5(b). Since such distribution members 81 are provided at oppositeends of the push-button 5, a pressing load from the push button 5 isevenly distributed by the distribution members 81 whatever portion ofthe push button 5 may be depressed. Hence, it is ensured that thec-contacts 9 a, 9 b are opened/closed at a time.

[0108] Next, the operations of the push-button switch 1 of the abovearrangement will be described with reference to FIGS. 1 to 4.

[0109] When the push button 5 in the first OFF state shown in FIG. 1 isdepressed, both of the switching mechanisms 11 a, 11 b operate asfollows. The pressing shafts 63 a, 63 b move down in conjunction withthe push button 5 while the slopes 71 a, 71 b thereof are locked to theslopes 79 a, 79 b of the slide blocks 61 a, 61 b. On the other hand, thedepression of the push button 5 brings the second ends 77 a, 77 b of theslide blocks 61 a, 61 b into abutment against the upper ends of thepressing sections 37 a, 37 b, thereby pressing down the pressingsections 37 a, 37 b. Thus, the first ends 39 a, 39 b of the operativemembers 43 a, 43 b are pressed downward against the helical springs 45a, 45 b.

[0110] When the operative members 43 a, 43 b of the c-contacts 9 a, 9 bare pressed downward in this manner, the first ends 39 a, 39 b of theoperative members 43 a, 43 b are rotated downward about the second ends41 a, 41 b thereof. Such a rotation expands the helical springs 45 a, 45b. When the amount of rotation of the first ends 39 a, 39 b of theoperative members 43 a, 43 b reaches a first dead point at which theupward urging force of the helical springs 45 a, 45 b on the first endsof the movable terminals 31 a, 31 b is changed to a downward urgingforce, the movable terminals 31 a, 31 b rotate downward about the secondends 29 a, 29 b thereof leaving the normally close stationary terminals33 a, 33 b to come into contact with the normally open stationaryterminals 35 a, 35 b. Thus, the push-button switch 1 is shifted from thefirst OFF state to the ON state.

[0111] At this time, the change of the urging direction of the helicalsprings 45 a, 45 b causes the movable terminals 31 a, 31 b to move tothe normally open stationary terminals 35 a, 35 b, so that the tactileclick-touch is produced. This permits the operator to recognize that thepush-button switch 1 has been shifted from the first OFF state to the ONstate.

[0112] During the transition from the first OFF state to the ON state,the slopes 79 a, 79 b of the slide blocks 61 a, 61 b are subjected to apressure from the slopes 71 a, 71 b of the pressing shafts 63 a, 63 b,the pressure acting to push the slide blocks 61 a, 61 b toward the outersides of the push button 5. However, the force of the helical springs 75a, 75 b for urging the slide blocks 61 a, 61 b toward the center of thepush button 5 is greater than this pressure, so that the slide blocks 61a, 61 b are not moved toward the opposite ends of the push-button 5.Thus, the pressing shafts 63 a, 63 b together with the slide blocks 61a, 61 b are moved downward as interlocked with the push button 5.

[0113] If the depression of the push button 5 in the ON state is eased,the upward movement of the push button 5 involves an upward movement ofthe pressing sections 37 a, 37 b. This releases the pressure of thepressing sections 37 a, 37 b on the operative members 43 a, 43 b so thatthe first ends 39 a, 39 b of the operative members 43 a, 43 b rotateupwardly.

[0114] When the amount of rotation of the first ends 39 a, 39 b of theoperative members 43 a, 43 b reaches a second dead point at which thedownward urging force of the helical springs 45 a, 45 b on the movableterminals 31 a, 31 b is changed to the upward urging force, the movableterminals 31 a, 31 b rotate upwardly about the second ends 29 a, 29 bthereof leaving the normally open stationary terminals 35 a, 35 b tocome into contact with the normally close stationary terminals 33 a, 33b. Thus, the push-button switch 1 is returned from the ON state to thefirst OFF state.

[0115] In the c-contacts 9 a, 9 b, a relation between the first deadpoint and the second dead point is defined as follows. As shown in FIG.6, the amount of rotation of the first end 39 a, 39 b of the operativemember 43 a, 43 b to reach the first dead point due to the increasedload on the operative member 43 a, 43 b is defined to be greater thanthe amount of rotation of the first end 39 a, 39 b of the operativemember 43 a, 43 b to reach the second dead point due to the decreasedload on the operative member 43 a, 43 b.

[0116] Accordingly, the amount of depression of the push button 5 toreturn the push-button switch 1 from the ON state to the first OFF stateis defined to be smaller than the amount of depression of the pushbutton 5 to shift the push-button switch 1 from the first OFF state tothe ON state. Hence, even if the depression of the push button 5 iseased, the push-button switch 1 is maintained in the ON state so long asthe decrease of the depression is within a predetermined range or unlessthe amount of rotation of the operative member 43 a, 43 b reaches thesecond dead point. Thus, the push-button switch 1 is prevented frombeing inadvertently shifted to the first OFF state.

[0117] Then, further depressing the push button 5 in the ON state shownin FIG. 2 brings the lower ends of the pressing shafts 63 a, 63 b intoabutment against the upper surfaces of the partitioning walls 25 a, 25b, as shown in FIG. 3. Still further depressing the push button 5 causesthe partitioning walls 25 a, 25 b to push up the pressing shafts 63 a,63 b so that the flanges 69 a, 69 b of the pressing shafts 63 a, 63 bare disengaged from the circumferences of the through holes 67 a, 67 bin the partitioning plates 53 a, 53 b.

[0118] In this process, the pressure on the slopes 79 a, 79 b of theslide blocks 61 a, 61 b from the slopes 71 a, 71 b of the pressingshafts 63 a, 63 b surpasses the urging force of the helical springs 75a, 75 b so that the slopes 79 a, 79 b of the slide blocks 61 a, 61 bslide on the slopes 71 a, 71 b of the pressing shafts 63 a, 63 b. Thus,the slide blocks 61 a, 61 b are slidably moved outwardly with respect tothe push button 5.

[0119] The outward slidable movement of the slide blocks 61 a, 61 bbrings the second ends 77 a, 77 b of the slide blocks 61 a, 61 b out ofthe abutment against the pressing sections 37 a, 37 b, therebypermitting an upward movement of the pressing sections 37 a, 37 b. Thus,the operative members 43 a, 43 b become free from the pressure from thepressing sections 37 a, 37 b. Thus, the switching mechanisms 11 a, 11 baccording to this embodiment constitute releasing means of the presentinvention.

[0120] When the operative members 43 a, 43 b are released from thepressure from the pressing sections 37 a, 37 b, the first ends 39 a, 39b of the operative members 43 a, 43 b are urged upward into rotation bythe helical springs 45 a, 45 b. The rotation of the first ends 39 a, 39b of the operative members 43 a, 43 b changes the downward urging forceon the first ends of the lovable terminals 31 a, 31 b to the upwardurging force, which, in turn, upwardly rotates the first ends of themovable terminals 31 a, 31 b. Thus, the movable terminals 31 a, 31 b incontact with the normally open stationary terminals 35 a, 35 b are movedaway therefrom to come into contact with the normally close stationaryterminals 33 a, 33 b, as shown in FIG. 4. As a result, the push-buttonswitch 1 is shifted from the ON state to the second OFF state.

[0121] In the second OFF state, the pressing member 51 of the pushbutton 5 abuts against an upper end of the movable member 15 of thenormally close contact 7 to press down the movable member 15, as shownin FIG. 4. Hence, the movable terminals 17 a, 17 b and the stationaryterminals 19 a, 19 b of the normally close contact 7 are forciblyseparated from each other. Therefore, even if the movable terminals 17a, 17 b should be fused with the stationary terminals 19 a, 19 b, forexample, the normally close contact 7 is assuredly shifted to the openstate because the movable terminals 17 a, 17 b are forcibly separatedfrom the stationary terminals 19 a, 19 b. Thus, the combination of thepressing member 51 and the movable member 15 according to thisembodiment constitutes forcible separation means of the presentinvention.

[0122] An example of circuit connections of the push-button switch 1 ofthe above arrangement will be described with reference to FIG. 7. It isnoted that the symbols ‘NC1’ and ‘NC2’ in FIG. 7 represent the normallyclose stationary terminals 33 a, 33 b of the c-contacts 9 a, 9 b,respectively; ‘NO1’ and ‘NO2’ representing the normally open stationaryterminals 35 a, 35 b, respectively; ‘C1’ and ‘C2’ representing themovable terminals 31 a, 31 b, respectively; ‘NC3’ representing thestationary terminals 19 a, 19 b of the normally close contact 7. A firstand a second circuits comprise the c-contacts 9 a, 9 b, respectively.More specifically, the respective pair of the normally open stationaryterminal 35 a, 35 b (NO1, NO2) and the movable terminal 31 a, 31 b (C1,C2) of the c-contact 9 a, 9 b constitute the first and the secondcircuits.

[0123] As shown in FIG. 7(a), when the push-button switch 1 is in thefirst OFF state, the first and the second circuits formed by thec-contacts 9 a, 9 b are in an OFF state with their C1 and C2 switched toNC1 and NC2, respectively. On the other hand, a third circuit formed bythe normally close contact 7 is in an ON state with its NC3 closed.

[0124] When the push button 5 is depressed, the first and the secondcircuits are shifted to the ON state with their C1 and C2 switched toNO1 and NO2, respectively, as shown in FIG. 7(b). Thus, the push-buttonswitch 1 is shifted to the ON state, in which the third circuitmaintains the ON state with its NC3 closed.

[0125] Then, a further depression of the push button 5 shifts the firstand the second circuits to the OFF state with their C1 and C2 switchedto NC1, NC2, respectively. Thus, the push-button switch 1 is shifted tothe second OFF state in which the third circuit is shifted to the OFFstate with its NC3 forcibly opened by the forcible separation means.

[0126] The push-button switch 1 has such an arrangement that the firstand the second circuits (9 a), (9 b) are simultaneously turned ON or OFFby depressing the push button 5 and that both the circuits assume the ONor OFF state at a time in correspondence to the first OFF state, the ONstate or the second OFF state. Therefore, it may be determined thateither one of the first circuit (9 a) and the second circuit (9 b) is infailure if the circuits, when monitored, are not in the ON or OFF statein unison.

[0127] When the push-button switch 1 is in the first or second OFFstate, both the first and the second circuits (9 a), (9 b) are in theOFF state. Hence, it is impossible to determine the push-button switch 1to be in the first OFF state or in the second OFF state by simplymonitoring the ON/OFF state of the first and second circuits.

[0128] On the other hand, the third circuit (7) assumes different statesin correspondence to the first OFF state and the second OFF state.Specifically, when the third circuit (7) is close, the push-buttonswitch 1 is in the first OFF state. When the third circuit (7) is open,the push-button switch 1 is in the second OFF state. Accordingly,whether the push-button switch 1 is in the first OFF state or in thesecond OFF state can be determined by monitoring the open/close state ofthe third circuit (7).

[0129] Now referring to FIG. 8, description will be made on a relationbetween the operation stroke and the operating load applied to the pushbutton 5 during the manipulation of the push-button switch 1. It isnoted that the numerals in circle correspond to the numbers of thedrawings, respectively.

[0130] As seen in FIG. 8, during a time period between the first OFFstate, which is the initial state, and the ON state or during atransition from the state ({circle over (1)}) shown in FIG. 1 to thestate ({circle over (2)}) shown in FIG. 2, the operating loadprogressively increases with increase in the operation stroke due to thedepression of the push button 5. The operating load originates in theurging force of the helical springs 59 a, 59 b disposed on the oppositesides of the push button 5.

[0131] During the subsequent transition from the state ({circle over(2)}) shown in FIG. 2 to the state ({circle over (3)}) shown in FIG. 3,the operation stroke by depressing the push button 5 increases littlewhereas the operating load increases sharply. This is because a greatload is required for horizontally moving the slide blocks 61 a, 61 b.

[0132] During the subsequent transition from the state ({circle over(3)}) shown in FIG. 3 to the state ({circle over (4)}) shown in FIG. 4,the operating load drops abruptly. This is because the pressing shafts63 a, 63 b are disengaged from the slide blocks 61 a, 61 b. That is, itis rather preferred that the push button 5 provides a lighter touch ifthe operator, manipulating the push-button switch in the ON state,should panic to depress the push button 5 strongly. Hence, a smoothtransition from the ON state to the second OFF state is provided bysetting such a small operating load.

[0133] When the push button in the state ({circle over (4)}) shown inFIG. 4 is further depressed, the operating load progressively increaseswith increase in the operation stroke. The operating load originates inthe urging force of the helical springs 59 a, 59 b disposed on theopposite sides of the push button 5 and of the helical springs 65 a, 65b disposed in the pressing shafts 63 a, 63 b.

[0134] According to the first embodiment of the present invention, asingle case contains therein two c-contacts 9 a, 9 b which aresimultaneously opened or closed by depressing the push button 5.Therefore, even if one of the contacts fails during the manipulation ofthe push-button switch 1, for instance, the other contact is capable ofturning ON/OFF the push-button switch 1. Thus, the push-button switch 1is enhanced in reliability. It is noted that the number of c-contact isnot limited to 2. Needless to say, a push-button switch including threeor more c-contacts can achieve a similar effect.

[0135] The c-contacts 9 a, 9 b have the snap action configurations andare arranged such that the amount of depression of the push button 5 toseparate the movable terminals 31 a, 31 b from the normally openstationary terminals 35 a, 35 b is smaller than the amount of depressionof the push button 5 to bring the movable terminals 31 a, 31 b intocontact with the normally open stationary terminals 35 a, 35 b.Therefore, even if the depression of the push button 5 is eased whilethe push-button switch 1 is in the ON state, the push-button switch 1 ismaintained in the ON state so long as the decrease of the depression iswithin a predetermined range or unless the amount of rotation of theoperative members 43 a, 43 b reaches the second dead point. Thisprevents the push-button switch from being inadvertently shifted to thefirst OFF state.

[0136] By virtue of the snap action configurations of the c-contacts 9a, 9 b, a proper tactile click-touch or a proper click sound is producedwhen the push-button switch 1 is shifted from the first OFF state to theON state or from the ON state to the second OFF state. Hence, theoperator depressing the push button 5 can readily determine whether ornot the push-button switch 1 is in the ON state permitting the dataentry.

[0137] Since the normally close contact 7 is provided, the first OFFstate or the second OFF state of the push-button switch 1 can bedistinguished based on the open/close state of the normally closecontact 7. In this case, the normally close contact 7 is not necessarilyconfigured to be open when the push-button switch 1 is in the second OFFstate, as described above. The normally close contact 7 may beconfigured to be opened when the push-button switch 1 is in the ON stateand to maintain the open state when the push-button switch 1 is shiftedto the second OFF state.

[0138] In the first embodiment described above, the third circuit (seeFIG. 7) formed by the normally close contact 7 is independent.Alternatively, the push-button switch 1 may comprise two circuits, asshown in FIG. 9, wherein this normally close contact 7 is connected inseries with the second circuit formed by one of the c-contacts 9 a (9b).

[0139] Similarly to the above embodiment, such an arrangement permitsthe first OFF state to be distinguished from the second OFF state bymonitoring the open/close state of the normally close contact 7.

[0140] In the first embodiment described above, both the first circuit(9 a) and the second circuit (9 b) formed by the c-contacts comprisesthe normally open stationary terminals 35 a, 35 b (NO1, NO2) and themovable terminals 31 a, 31 b (C1, C2), respectively. As shown in FIG.10, an alternative arrangement may be made such that the second circuitshown in FIG. 9 comprises the normally close stationary terminal 33 b(NC2) and the movable terminal 31 b (C2) of the c-contact 9 b and thatthe first circuit is adapted to be sequentially shifted to the first OFFstate, the ON state and the second OFF state according to threepositions of the push-button switch 1 whereas the second circuit isadapted to be sequentially shifted to the ON state, OFF state and the ONstate. That is, the first and the second circuits always assume theopposite ON/OFF positions according to the three positions of thepush-button switch.

[0141] Such an arrangement facilitates the determination that either oneof the c-contacts 9 a, 9 b forming the circuits is in failure when boththe first and the second circuits are ON or OFF at a time. In such acase, which of the c-contacts 9 a, 9 b is in failure can be determinedby monitoring these contacts alternately.

[0142] In the circuit connections shown in FIG. 10, the first OFF stateof the push-button switch 1 can be distinguished from the second OFFstate thereof by monitoring the open/close state of the normally closecontact 7 just as in the first embodiment described above.

[0143] The above first embodiment is described by way of the exampleincluding one normally close contact 7. Alternatively, the normallyclose contact may be provided in correspondence to each of thec-contacts 9 a, 9 b. Such an arrangement permits the determination ofthe ON/OFF state of each of the c-contacts 9 a, 9 b.

[0144] In the first embodiment described above, the normally closecontact 7 is provided as an auxiliary contact serving for the purpose ofdistinguishing the first OFF state from the second OFF state of thepush-button switch 1. Alternatively, for example, there may be provideda normally open contact adapted to be switched between an open positionand a close position according to the first OFF state and the second OFFstate.

[0145] (Second Embodiment)

[0146] A second embodiment of the present invention will be describedwith reference to FIGS. 11 to 13. FIGS. 11 to 13 are sectional frontviews of the second embodiment in different states for explaining theoperations thereof. It is noted that the same reference characters as inthe first embodiment described above represent the same or equivalentparts, respectively.

[0147] In this embodiment, essential configurations of the c-contacts 9a, 9 b are the same as those of the first embodiment and hence, thedescription of the like parts is dispensed with. The followingdescription principally focuses on differences from the firstembodiment.

[0148] As shown in FIG. 11, a push-button switch 101 of this embodimentdiffers from the first embodiment in configurations of a switch case103, a switching mechanism 107 disposed in a push button 105, andnormally close contacts 109 a, 109 b.

[0149] Within the switch case 103, two normally close contacts 109 a,109 b are disposed at a central lower portion thereof, whereas a pair ofc-contacts 9 a, 9 b of the above configurations are disposed at theopposite ends of the case as sandwiching the normally close contacts 109a, 109 b therebetween. An inside wall of the switch case 103 isintegrally formed with partitioning walls 111 a, 111 b extended over therespective upper portions of the c-contacts 9 a, 9 b.

[0150] Each of the normally close contacts 109 a, 109 b essentially hasthe same configuration as that of the normally close contact 7 of thefirst embodiment described above. As shown in FIG. 11, the normallyclose contacts 109 a, 109 b each comprise a movable member 110 a, 110 b;a movable terminal (not shown) attached to the movable member; and astationary terminal (not shown) adapted to be in or out of contact withthe movable terminal.

[0151] The normally close contacts 109 a, 109 b are provided withhelical springs 112 a, 112 b for urging upward the movable members 110a, 110 b, respectively. When the push button 105 is undepressed, thenormally close contacts 109 a, 109 b are close with the stationaryterminals being in contact with the movable terminals.

[0152] The push button 105 is formed with an accommodating portion 113vertically extended as defining a rectangular space in plan. Theaccommodating portion 113 contains therein the switching mechanism 107for opening/closing the c-contacts 9 a, 9 b.

[0153] The switching mechanism 107 comprises pressing sections 115 a,115 b for depressing operative members 43 a, 43 b of the c-contacts 9 a,9 b; a pair of slide blocks 117 a, 117 b for pressing down the pressingsections 115 a, 115 b as interlocked with the depression of the pushbutton 105; and pressing shafts 121 a, 121 b urged downwardly by helicalsprings 119 a, 119 b attached to an upper wall of the accommodatingportion 113.

[0154] The pressing shaft 121 a, 121 b is disposed between apartitioning plate 123 a, 123 b and an end of the accommodating portion113, the partitioning plate having an L-shaped section and extendingdownward from the upper wall of the accommodating portion 113 of thepush button 105. The pressing shaft 121 a, 121 b has a hollow structure,whereas a lower end of the above helical spring 119 a, 119 b is fixed toa bottom of the hollow structure.

[0155] The slide blocks 117 a, 117 b are centrally located in the pushbutton 105 in a manner to contact with each other, as allowed to movehorizontally (the transverse direction as seen in FIG. 11). The slideblock 117 a, 117 b is formed with a cavity 125 a, 125 b verticallyextended therethrough, whereas a pendent portion 127 a, 127 b extendsfrom an upper inside surface of the accommodating portion 113 throughthe cavity 125 a, 125 b.

[0156] The slide block 117 a, 117 b is formed with a slope 129 a, 129 bat a lower portion of a first end thereof. The slopes 129 a, 129 b areadapted for engagement with slopes at an upper end of a pressing member131 to be described hereinafter. On the other hand, a helical spring 133a, 133 b is seated between an inside wall of the first end of the slideblock 117 a, 117 b and the pendent portion 127 a, 127 b. Thus, the slideblocks 117 a, 117 b are urged toward the center of the push button 105by means of the helical springs 133 a, 133 b.

[0157] The pendent portion 127 a, 127 b presents its lower end into agap 135 a, 135 b defined in the partitioning plate 123 a, 123 b. On theother hand, the pressing section 115 a, 115 b extends downward with itsupper end inserted through a clearance defined by the pendent portion127 a, 127 b inserted in the gap 135 a, 135 b.

[0158] The upper end of the pressing section 115 a, 115 b is adapted toabut against a second end 137 a, 137 b of the slide block. When theslide block 117 a, 117 b is moved downward as interlocked with thedepression of the push button 105, the second end 137 a, 137 b of theslide block 117 a, 117 b abuts against the upper end of the pressingsection 115 a, 115 b to move down the pressing section 115 a, 115 b.

[0159] The partitioning plate 123 a, 123 b is integrally formed with aprojection 139 a, 139 b on a lower surface near a center-side endthereof, the projection being shaped like

in section. The projection 139 a, 139 b descends in conjunction with thedownward movement of the slide block 117 a, 117 b and abuts against themovable member 110 a, 110 b of the normally close contact 109 a, 109 bso as to press down the movable member.

[0160] In the initial state, the slide blocks 117 a, 117 b are incontacting relation as urged toward the center of the push button 105 bymeans of the helical springs 133 a, 133 b. In this state, the slopes 129a, 129 b of the slide blocks 117 a, 117 b define a triangular recess 141in section.

[0161] The pressing member 131 with a beak-like upper end is locatedbelow the recess 141 as spaced a predetermined distance therefrom. Whenthe slide blocks 117 a, 117 b are depressed via the push button 105, theupper end of the pressing member 131 enters a space between thecenter-side ends of the partitioning plates 123 a, 123 b to come intoengagement with the recess 141. Thus, the pressing member 131 is adaptedto distend the slide blocks 117 a, 117 b as the depression of the pushbutton 105 is increased.

[0162] The operations of the push-button switch of the above arrangementwill be described with reference to FIGS. 11 to 13.

[0163] When the push button 105 in the first OFF state shown in FIG. 11is depressed, the second ends 137 a, 137 b of the slide blocks 117 a,117 b come into abutment against the upper ends of the pressing sections115 a, 115 b so as to push down the pressing sections 115 a, 115 b, asshown in FIG. 12.

[0164] The pressing sections 115 a, 115 b thus depressed depress thefirst ends 39 a, 39 b of the operative members 43 a, 43 b of thec-contacts 9 a, 9 b against the helical springs 45 a, 45 b, therebydownwardly rotating the first ends 39 a, 39 b of the operative members43 a, 43 b. When the amount of rotation of the operative members reachesthe first dead point at which the upward urging force of the helicalsprings 45 a 45 b on the first ends of the movable terminals 31 a, 31 bis changed to the downward urging force, the movable terminals 31 a, 31b of the c-contacts 9 a, 9 b rotate downwardly about the second ends 29a, 29 b thereof, as shown in FIG. 12. Thus, the movable terminals 31 a,31 b are separated from the normally close stationary terminals 33 a, 33b to come into contact with the normally open stationary terminals 35 a,35 b, so that the push-button switch 101 is shifted from the first OFFstate to the ON state.

[0165] At this time, the upper end of the pressing member 131 is engagedwith the recess 141 defined by the pair of slide blocks 117 a, 117 b.When the push button 105 in this state is further depressed, the slopesat the upper end of the pressing member 131 slide on the slopes 129 a,129 b of the slide blocks 117 a, 117 b, as shown in FIG. 13, therebyslidably moving the slide blocks 117 a, 117 b outwardly with respect tothe push button 105. This involves an outward movement of the secondends 137 a, 137 b of the slide blocks 117 a, 117 b with respect to thepush button 105, so that the second ends 137 a, 137 b of the slideblocks 117 a, 117 b are brought out of the abutment against the pressingsections 115 a, 115 b. The pressing sections 115 a, 115 b, in turn, areallowed to move upward so as to release the pressure upon the operativemembers 43 a, 43 b. Thus, the switching mechanism 107 according to thisembodiment constitutes the releasing means of the present invention.

[0166] When the operative members 43 a, 43 b are released from thepressure from the pressing sections 115 a, 115 b, the first ends 39 a,39 b of the operative members 43 a, 43 b are urged upward into rotationby the helical springs 45 a, 45 b, as shown in FIG. 13. The rotation ofthe first ends 39 a, 39 b of the operative members 43 a, 43 b changesthe downward urging force on the first ends of the movable terminals 31a, 31 b to the upward urging force, which upwardly rotates the firstends of the movable terminals 31 a, 31 b. Thus, the movable terminals 31a, 31 b in contact with the normally open stationary terminals 35 a, 35b are separated therefrom to come into contact with the normally closestationary terminals 33 a, 33 b, so that the push-button switch 101 isshifted from the ON state to the second OFF state.

[0167] At this time, the projections 139 a, 139 b depress the movablemembers 110a, 110 b of the normally close contacts 109 a, 109 b toseparate the movable terminals from the stationary terminals so that thenormally close contacts 109 a, 109 b are opened. Even if the movableterminals are fused with the stationary terminals at this time, thedepressing projections 139 a, 139 b forcibly separate the movableterminals from the stationary terminals.

[0168] The amount of depression of the push button 105 to shift thepush-button switch 101 from the ON state to the first OFF state is setsmaller than the amount of depression to shift the switch from the firstOFF state to the ON state. Hence, even if the depression of the pushbutton 105 is eased, the push-button switch 101 is maintained in the ONstate so long as the decrease in the depression of the push button iswithin the predetermined range or unless the amount of rotation of theoperative members 43 a, 43 b reaches the second dead point. Thus,similarly to the first embodiment described above, the push-buttonswitch is prevented from being inadvertently shifted to the first OFFstate and is also adapted to provide the tactile click-touch or clicksound.

[0169] According to the second embodiment, an equal effect to that ofthe first embodiment described above is naturally achieved. Furthermore,the second embodiment features a simple configuration because a singlepressing member 131 is used to effect the horizontal movement of theslide blocks 117 a, 117 b for releasing the operative members 43 a, 43 bfrom the depression by the pressing sections 115 a, 115 b. As a result,the push-button switch 101 accomplishes cost reduction.

[0170] The second embodiment described above is provided with twonormally close contacts 109 a, 109 b such that whether the c-contact 9a, 9 b are in the first OFF state or the second OFF state can bedetermined by monitoring the open/close state of the normally closecontacts 109 a, 109 b.

[0171] In the second embodiment described above, the first and thesecond circuits formed by the c-contacts 9 a, 9 b may have the same wireconnections as those shown in FIG. 7 or 10 illustrating the firstembodiment. An alternative circuit configuration may be made such thatthe first and the second circuits formed by the c-contacts 9 a, 9 b areconnected in series with the normally close contacts 109 a, 109 b,respectively.

[0172] (Third Embodiment)

[0173] A third embodiment of the present invention will be describedwith reference to FIGS. 14 to 17. FIGS. 14 to 17 are sectional frontviews of the third embodiment in different states for explaining theoperations thereof. It is noted that the same reference characters as inthe first embodiment described above represent the same or equivalentparts, respectively.

[0174] In this embodiment, essential configurations of the c-contacts 9a, 9 b are the same as those of the first embodiment and hence, thedescription of the like parts is dispensed with. The followingdescription principally focuses on differences from the firstembodiment.

[0175] As shown in FIG. 14, a push-button switch 151 of this embodimentdiffers from that of the first embodiment in the configurations of aswitch case 152, a switching mechanism 154 disposed in a push button 153and normally close contacts 155 a, 155 b. In this embodiment, a rubbercover 156 and an external button 157 are attached to the push button 153in a manner to cover the same.

[0176] The switch case 152 is centrally provided with an accommodationmember 161 at a lower portion thereof, the accommodation member 161including two accommodating portions 160a, 160 b. The accommodatingportions 160 a, 160 b contain therein the normally close contacts 155 a,155 b, respectively. Disposed on the opposite sides of the accommodationmember 161 are a pair of c-contacts 9 a, 9 b of the above configuration.Similarly to the first embodiment, an inside wall of the switch case 152is integrally formed with L-shaped partitioning walls 162 a, 162 b insection, which extend over the upper parts of the c-contacts 9 a, 9 b,respectively.

[0177] The normally close contacts 155 a, 155 b are essentiallyconfigured the same way as the normally close contact 7 of the firstembodiment described above. As shown in FIG. 14, the normally closecontacts 155 a, 155 b each comprise a movable member 164 a, 164 bprojecting from a through hole 163 a, 163 b formed in an upper side ofthe accommodation member 161; a movable terminal pair 166 a, 166 battached to a lower end of the movable member 164 a, 164 b via aconductive member 165 a, 165 b; and a stationary terminal pair 167 a,167 b adapted to be in or out of contact with the movable terminal pair166 a, 166 b.

[0178] The movable member 164 a, 164 b has a helical spring 168 a, 168 bmounted to its lower end for urging the movable member 164 a, 164 bupwardly. When the push button 153 is undepressed, the normally closecontact 155 a, 155 b is closed with its stationary terminal pair 167 a,167 b and the movable terminal pair 166 a, 166 b held in contact witheach other by means of an urging force of the helical spring 168 a, 168b.

[0179] The push button 153 is formed with an accommodating portion 170vertically extended as defining a rectangular space in plan. Theaccommodating portion 170 is centrally provided with a pressing plate173 fixed to an upper inside surface of the accommodating portion 170via two pairs of pendent members 171 a, 171 b, 172 a, 172 b. Theswitching mechanism 154 for opening/closing the c-contacts 9 a, 9 b isdisposed in an upper cavity 174 defined by the pressing plate 173 andthe upper inside surface of the accommodating portion 170. The pushbutton 153 is formed with screw holes 175 a, 175 b at opposite endsthereof for mounting the external button 157 and the rubber cover 156which will be described hereinafter.

[0180] The switching mechanism 154 comprises pressing sections 176 a,176 b for depressing the operative members 43 a, 43 b of the c-contacts9 a, 9 b; a pair of slide blocks 177 a, 177 b for pressing down thepressing sections 176 a, 176 b as interlocked with the depression of thepush button 153; a pressing shaft 180 in locked relation with the slideblocks 177 a, 177 b; and a pair of pressure bodies 182 a, 182 b urgeddownward by helical springs 181 a, 181 b attached to the upper insidesurface of the accommodating portion 170.

[0181] The pressing sections 176 a, 176 b extend downward from throughholes 183 a, 183 b defined at opposite ends of the pressing plate 173and abut against the first ends 39 a, 39 b of the operative members 43a, 43 b of the c-contacts 9 a, 9 b on their lower ends.

[0182] The pressing shaft 180 has a hollow structure. A helical spring184 attached to the upper inside surface of the accommodating portion170 has its lower end fixed to place in the pressing shaft 180, thusurging the pressing shaft 180 downwardly.

[0183] The pressing shaft 180 is inserted through a through hole 185formed centrally of the pressing plate 173, whereas a pair of flanges186 a, 186 b formed at an upper end of the pressing shaft 180 are lockedto the pressing plate 173 at a circumference of the through hole 185 sothat the pressing shaft 180 is restrained from moving downwardly(dropping-off). The flanges 186 a, 186 b of the pressing shaft 180 arerespectively formed with a slope 187 a, 187 b on a side surface thereof.

[0184] The slide block 177 a, 177 b is formed with a cavity 178 a, 178 bvertically extended therethrough, through which the center-side pendentmember 171 a, 171 b with respect to the push button 153 is extended. Theslide block 171 a, 171 b is slidably movable in the upper cavity 174along the horizontal direction (the transverse direction as seen in FIG.14) and urged toward the center of the push button 153 by a helicalspring 191 a, 191 b interposed between a first end 190 a, 190 b of theslide block 177 a, 177 b and the pendent member 171 a, 171 b extendedthrough the cavity 178 a, 178 b.

[0185] The slide block 177 a, 177 b is formed with a slope 192 a, 192 bat the first end 190 a, 190 b thereof, the slope 192 a, 192 b locked tothe slope 187 a, 187 b of the flange 186 a, 186 b of the pressing shaft180.

[0186] A second end 193 a, 193 b of the slide block 177 a, 177 b isadapted to abut against an upper end of the pressing section 176 a, 176b, so that the slide block 177 a, 177 b descends as interlocked with thedepressed push button 153, thereby pressing down the pressing section176 a, 176 b.

[0187] The pressure body 182 a, 182 b is interposed between apartitioning plate 194 a, 194 b and aside of the pressing plate 173, thepartitioning plate having an L-shaped section and extending downwardfrom an inside upper surface at each of the opposite ends of theaccommodating portion 170. The pressure body 182 a, 182 b has a hollowstructure whereas the helical spring 181 a, 181 b has its lower endfixed to a bottom of the hollow body.

[0188] Further, as shown in FIG. 14, the external button 157 is attachedto a top surface of the push button 153 fry via the rubber cover 156.The external button 157 is secured to the push button 153 with screws atopposite ends thereof. Such an arrangement prevents the deformation orbreakage of the top surface of the push button 153 because the pushbutton 153 is not directly depressed. The rubber cover 156 covers thetop surface of the push button 153 and has its opposite ends fixed tolower surfaces of flanges 196 a, 196 b on lateral sides of the switchcase 152. The watertightness of the push-button switch 151 is enhancedin this manner.

[0189] Next, the operations of the push-button switch 151 of the abovearrangement will be described with reference to FIGS. 14 to 17.

[0190] When the push button 153 in the first OFF state shown in FIG. 14is depressed, the second ends 193 a, 193 b of the slide blocks 177 a,177 b come into abutment against the upper ends of the pressing sections176 a, 176 b so as to press down the pressing sections 176 a, 176 b, asshown in FIG. 15.

[0191] The depressed pressing sections 176 a, 176 b, in turn, depressthe first ends 39 a, 39 b of the operative members 43 a, 43 b of thec-contacts 9 a, 9 b against the helical springs 45 a, 45 b, therebydownwardly rotating the first ends 39 a, 39 b of the operative members43 a, 43 b. When the amount of rotation of the operative members reachesthe first dead point at which the upward urging force of the helicalsprings 45 a, 45 b on the first ends of the movable terminals 31 a, 31 bis changed to the downward urging force, the movable terminals 31 a, 31b of the c-contacts 9 a, 9 b rotate downwardly about the second ends 29a, 29 b thereof, as shown in FIG. 15. Thus, the movable terminals 31 a,31 b are separated from the normally close stationary terminals 33 a, 33b to come into contact with the normally open stationary terminals 35 a,35 b so that the push-button switch 151 is shifted from the first OFFstate to the ON state.

[0192] During the transition from the first OFF state to the ON state,the slopes 187 a, 187 b of the pressing shaft 180 apply a pressure tothe slopes 192 a, 192 b of the slide blocks 177 a, 177 b to drive theslide blocks 177 a, 177 b outwardly with respect to the push button 153.However, the pressure is surpassed by the force of the helical springs191 a, 191 b urging the slide blocks 177 a, 177 b toward the center ofthe push button 153, so that the slide blocks 177 a, 177 b are not movedtoward the opposite ends of the push button 153. Hence, the pressingshaft 180 together with the slide blocks 177 a, 177 b are moved downwardas interlocked with the push button 153.

[0193] At this time, the pressure bodies 182 a, 182 b have their bottomsabutted against the upper sides of the partitioning walls 162 a, 162 b.Therefore, further depressing the push button 153 in this state requiressuch a force as to overcome the urging force of the helical springs 181a, 181 b. This increases the load for further depressing the push button153 in the ON state.

[0194] When the push button 153 in the ON state as shown in FIG. 15 isfurther depressed, a lower end of the pressing shaft 180 comes intoabutment against the upper surface of the accommodation member 161, asshown in FIG. 16. When the push button 153 is still further depressed,the pressing shaft 180 is pushed up by the accommodation member 161 andhence, the flanges 186 a, 186 b of the pressing shaft 180 is disengagedfrom the circumference of the through hole 185 in the pressing plate173.

[0195] In this process, the pressure applied to the slopes 192 a, 192 bof the slide blocks 177 a, 177 b by the slopes 187 a, 187 b of thepressing shaft 180 surpasses the urging force of the helical springs 191a, 191 b, so that the slopes 192 a, 192 b of the slide blocks 177 a, 177b slide on the slopes 187 a, 187 b of the pressing shaft 180. Thus, theslide blocks 177 a, 177 b are slidably moved outwardly with respect tothe push button 153.

[0196] The outward sliding movement of the slide blocks 177 a, 177 bbrings the second ends 193 a, 193 b thereof out of the abutment againstthe pressing sections 176 a, 176 b. Thus, the pressing sections 176 a,176 b are allowed to move upward to release the pressure on theoperative members 43 a, 43 b. Thus, the switching mechanism 154according to this embodiment constitutes the releasing means of thepresent invention.

[0197] When the operative members 43 a, 43 b are released from thepressure of the pressing sections 176 a, 176 b, the first ends 39 a, 39b of the operative members 43 a, 43 b rotate upwardly as urged upward bythe helical springs 45 a, 45 b, as shown in FIG. 17. Because of therotation of the first ends 39 a, 39 b of the operative members 43 a, 43b, the downward urging force on the first ends of the movable terminals31 a, 31 b is changed to the upward urging force which upwardly rotatesthe first ends of the movable terminals 31 a, 31 b. Thus, the movableterminals 31 a, 31 b in contact with the normally open stationaryterminals 35 a, 35 b are separated therefrom to come into contact withthe normally close stationary terminals 33 a, 33 b. As a result, thepush-button switch 151 is shifted from the ON state to the second OFFstate.

[0198] In the second OFF state, the pressing plate 173 of the pushbutton 153 abuts against the upper ends of the movable members 164 a,164 b of the normally close contacts 155 a, 155 b to depress the movablemembers 164 a, 164 b, as shown in FIG. 17. Thus, the movable terminalpair 166 a, 166 b and the stationary terminal pair 167 a, 167 b of thenormally close contact 155 a, 155 b are forcibly separated from eachother. Therefore, if the movable terminal pair 166 a, 166 b are fusedwith the stationary terminal pair 167 a, 167 b, for example, the movableterminal pair 166 a, 166 b are forcibly separated from the stationaryterminal pair 167 a, 167 b to open the normally close contact 155 a, 155b. Thus, the combination of the pressing plate 173 and the movablemembers 164 a, 164 b constitutes the forcible separation means of thepresent invention.

[0199] According to the third embodiment, the equal effect to that ofthe first embodiment described above is naturally achieved. Furthermore,the third embodiment features a simple configuration because a singlepressing shaft 180 is used to effect the simultaneous horizontalmovement of the slide blocks 177 a, 177 b for releasing the operativemembers 43 a, 43 b from the depression by the pressing sections 176 a,176 b. As a result, the push-button switch 151 accomplishes costreduction.

[0200] The third embodiment described above is provided with twonormally close contacts 155 a, 155 b such that whether the c-contacts 9a, 9 b are in the first OFF state or in the second OFF state can bedetermined by monitoring the open/close state of the normally closecontacts 155 a, 155 b.

[0201] In the third embodiment described above, the first and the secondcircuits formed by the c-contacts 9 a, 9 b may have the same wireconnections as those shown in FIG. 7 or 10 illustrating the firstembodiment. An alternative circuit configuration may be made such thatthe first and the second circuits formed by the c-contacts 9 a, 9 b areconnected in series with the normally close contacts 155 a, 155 b,respectively.

[0202] (Fourth Embodiment)

[0203] A fourth embodiment of the present invention will be describedwith reference to FIGS. 18 to 21. FIGS. 18 to 21 are sectional frontviews of the fourth embodiment in different states for explaining theoperations thereof. It is noted that the same reference characters as inthe first embodiment represent the same or equivalent parts,respectively.

[0204] As shown in FIG. 18, a push-button switch 201 according to thisembodiment comprises a switch case 203 provided with two c-contacts 9 a,9 b of the same configurations as in the first embodiment; a cylindricalcase member 205 mounted to an upper end of the switch case 203; anoperating shaft 207 accommodated in the case member 205 foropening/closing the c-contacts 9 a, 9 b; and a push button 209 mountedto an upper end of the operating shaft 207.

[0205] The switch case 203 contains the tandem-arranged c-contacts 9 a,9 b in its lower part and is provided with a cylindrical engagementmember 211 which is disposed over the c-contacts 9 a, 9 b. Theengagement member 211 is formed with a taper 213 on an inside wall at anupper end thereof. The switch case 203 is formed with a pair of flanges215 a, 215 b on its outer side, which are secured to a teaching pendantor the like via screws or the like.

[0206] The operating shaft 207 disposed in the case member 205 comprisesa pair of pressing members 217 a, 217 b in opposed relation; and acoupling member 219 attached to upper ends of the pressing members 217a, 217 b for coupling the pressing members 217 a, 217 b with the pushbutton 209. A helical spring 223 is mounted about a lower part of thecoupling member 219, as anchored at one end to a step 220 formedcentrally of a periphery of the coupling member 219 and at the other endto a step 221 formed on an inside surface of the case member 205 atplace lower than a mid-portion thereof. The helical spring 223 urgesupwardly the push button 209, the coupling member 219 and the pressingmembers 217 a, 217 b.

[0207] The pressing member 217 a, 217 b includes a plate-like supportportion 225 a, 225 b extended vertically; and an engaging piece 227 a,227 b integrally formed with the support portion as extended from alower end thereof. The engaging piece 227 a, 227 b is formed with aslope 229 a, 229 b on its lower side, which is adapted for engagementwith the taper 213 at the upper end of the engagement member 211.

[0208] The engaging piece 227 a, 227 b of the pressing member 217 a, 217b is formed with a projecting piece 231 a, 231 b on a side thereof, theprojecting piece extended downwardly. The projecting piece 231 b of theleft-hand pressing member 217 b is longer than the projecting piece 231a of the right-hand pressing member 217 a. Disposed under the longerprojecting piece 231 b is a pressing section 233 for depressing theoperative members 43 a, 43 b of the two c-contacts 9 a, 9 b. Theprojecting piece 231 b abuts against an upper end of the pressingsection 233 to press down the pressing section 233, which, in turn,depresses the operative members 43 a, 43 b thereby operating thec-contacts 9 a, 9 b.

[0209] A helical spring 235 is disposed between lower portions of theopposing support portions 225 a, 225 b of the pressing members 217 a,217 b. The pressing members 217 a, 217 b are urged outwardly by thehelical spring 235.

[0210] Next, the operations of the push-button switch 201 of the abovearrangement will be described with reference to FIGS. 18 to 21.

[0211] When the push button 209 in the first OFF state shown in FIG. 18is depressed, the operating shaft 207 is depressed as interlocked withthe push button 209 while the longer projecting piece 231 b presses downthe pressing section 233, as shown in FIG. 19. Thus, the pressingsection 233 depresses the first ends 39 a, 39 b of the operative members43 a, 43 b of the c-contacts 9 a, 9 b against the helical springs 45 a,45 b whereby the first ends 39 a, 39 b of the operative members 43 a, 43b are rotated downwardly.

[0212] When the amount of rotation of the first ends 39 a, 39 b of theoperative members 43 a, 43 b reaches the first dead point at which theupward urging force of the helical spring 45 a, 45 b on the first endsof the movable terminals 31 a, 31 b is changed to the downward urgingforce, the movable terminals 31 a, 31 b of the c-contacts 9 a, 9 b arerotated downwardly about the second ends 29 a, 29 b thereof, as shown inFIG. 19. Thus, the movable terminals 31 a, 31 b are separated from thenormally close stationary terminals 33 a, 33 b to come into contact withthe normally open stationary terminals 35 a, 35 b. As a result, thepush-button switch 201 is shifted from the first OFF state to the ONstate.

[0213] When the push-button switch 201 in this state is furtherdepressed, the engaging pieces 227 a, 227 b of the pressing members 217a, 217 b enter a hollow portion of the engagement member 211, as shownin FIG. 20. On the other hand, while the slopes 229 a, 229 b of theengaging pieces 227 a, 227 b slide on the taper 213 of the engagementmember 211, the projecting pieces 231 a, 231 b of the pressing members217 a, 217 b move toward the center of the push-button switch 201against the helical spring 235.

[0214] This brings the longer projecting piece 231 b out of the abutmentagainst the pressing section 233 which, in turn, is allowed to moveupwardly. Hence, the operative members 43 a, 43 b are released from thepressure from the pressing section 233. Thus, the combination of thepressing members 217 a, 217 b, the engagement member 211 and thepressing section 233 according to this embodiment constitutes thereleasing means of the present invention.

[0215] When the operative members 43 a, 43 b are released from thepressure from the pressing section 233, the first ends 39 a, 39 b of theoperative members 43 a, 43 b are rotated as urged upward by the helicalsprings 45 a, 45 b, as shown in FIG. 21. Because of the rotation of thefirst ends 39 a, 39 b of the operative members 43 a, 43 b, the downwardurging force on the first ends of the movable terminals 31 a, 31 b ischanged to the upward urging force, which upwardly rotates the firstends of the movable terminals 31 a, 31 b. Hence, the movable terminals31 a, 31 b in contact with the normally open stationary terminals 35 a,35 b are separated therefrom to come into contact with the normallyclose stationary terminals 33 a, 33 b. Thus, the push-button switch 201is shifted from the ON state to the second OFF state.

[0216] According to the fourth embodiment, the equal effect to that ofthe first embodiment described above is naturally achieved. Furthermore,the fourth embodiment features a simple on figuration for switching thepush-button switch 201 between the ON state and the OFF state because asingle pressing member 217 b is used for depressing or releasing thepressing section 233. As a result, the push-button switch 201accomplishes cost reduction.

[0217] Although the normally close contact (or the normally opencontact) is not shown in FIGS. 18 to 21, such a contact may naturally beprovided in the case 205. In this case, there may be provided a singlenormally close contact (or normally open contact). Otherwise, anindividual normally close contact (or normally open contact) may beprovided in correspondence to each of the c-contacts 9 a, 9 b.

[0218] In the fourth embodiment described above, as well, the first andthe second circuits formed by the c-contacts 9 a, 9 b may have the samewire connections as those shown in FIG. 7 or 10 illustrating the firstembodiment. An alternative circuit configuration may be made such thatthe first and the second circuits formed by the c-contacts 9 a, 9 b areconnected in series with the normally close contact.

[0219] (Fifth Embodiment)

[0220] A fifth embodiment of the present invention will be describedwith reference to FIGS. 22 to 25. FIGS. 22 to 25 are sectional frontviews of the fifth embodiment in different states for explaining theoperations thereof. It is noted that the same reference characters as inthe first embodiment represent the same or equivalent parts,respectively.

[0221] As shown in FIG. 22, a push-button switch 301 according to thisembodiment comprises a switch case 303; a push button 305 depressiblysupported by the switch case 303; the c-contacts 9 a, 9 b disposed inthe switch case 303 and having the same configurations as in the firstembodiment; the normally close contact (not shown) disposed in theswitch case 303 and having the same configuration as in the secondembodiment; and a switching mechanism 309 disposed in the push button305 for opening/closing the c-contacts 9 a, 9 b.

[0222] As shown in FIG. 22, the switch case 303 has its lower portiondivided into two accommodating portions 313, 315 by a partitioning plate311. The left-hand accommodating portion 313 accommodates thetandem-arranged c-contacts 9 a, 9 b whereas the right-hand accommodatingportion 315 accommodates the normally close contact (not shown).

[0223] An interior of the push button 305 defines a rectangularaccommodating portion 317 in plan, in which the switching mechanism 309is disposed. The switching mechanism 309 comprises a pressing section321 for depressing the first ends 39 a, 39 b of the operative members 43a, 43 b of the c-contacts 9 a, 9 b; and a pressing member 323 forpressing down the pressing section 321.

[0224] The pressing member 323 is shaped like a box with an open top. Ahelical spring 319, fixed to an upper wall of the accommodating portion317, is anchored at lower end thereof to a bottom of the interior spaceof the pressing member 323. The pressing section 321 is urged downwardlyby the helical spring 319. A horizontal portion 325 defining a bottom ofthe pressing member 323 is formed with a pair of slopes 327 a, 327 b atopposite ends of a lower side thereof.

[0225] The pressing member 323 is integrally formed with a projectingpiece 329 at an upper left end thereof. The pressing member 323 isarranged such that the projecting piece 329 is in engagement with anupper end of the pressing section 321 when the push button 305 isundepressed. Depressing the push button 305 involves a downward movementof the pressing member 323 such that the projecting piece 329 abutsagainst the pressing section 321 to depress the pressing section 321.

[0226] As indicated by the broken line in FIG. 22, a locking piece 333having an arcuate portion 331 at its upper end is formed on an outsidefront surface of the pressing member 323. The arcuate portion 331 of thelocking piece 333 is locked to a step 337 formed on an inside front wallof the push button 305 and including a slope 335 extended downward asinclined leftwardly.

[0227] The operations of the push-button switch of the above arrangementwill be described with reference to FIGS. 22 to 25.

[0228] When the push button 305 in the first OFF state shown in FIG. 22is depressed, the pressing member 323 urged downward by the helicalspring 319 moves down as interlocked with the push button 305, as shownin FIG. 23. In conjunction with the movement of the pressing member 323,the projecting piece 329 thereof presses down the pressing section 321.Thus, the pressing section 321 depresses the first ends 39 a, 39 b ofthe operative members 43 a, 43 b of the c-contacts 9 a, 9 b against thehelical springs 45 a, 45 b, so that the first ends 39 a, 39 b of theoperative members 43 a, 43 b are rotated downwardly.

[0229] When the amount of rotation of the first ends 39 a, 39 b of theoperative members 43 a, 43 b reaches the first dead point at which theupward urging force of the helical springs 45 a, 45 b on the first endsof the movable terminals 31 a, 31 b is changed to the downward urgingforce, the movable terminals 31 a, 31 b of the c-contacts 9 a, 9 b arerotated downward about the second ends 29 a, 29 b thereof, as shown inFIG. 23. Thus, the movable terminals 31 a, 31 b are separated from thenormally close stationary terminals 33 a, 33 b to come into contact withthe normally open stationary terminals 35 a, 35 b. As a result, thepush-button switch 201 is shifted from the first OFF state to the ONstate.

[0230] At this time, the horizontal portion 325 at the bottom of thepressing member 323 abuts against the top surface of the partitioningplate 311. When the push button 305 in this state is further depressed,the arcuate portion 331 of the locking piece 333 on the pressing member323 slides on the slope 335 of the step 337 formed on the inside wall ofthe push button 305, as shown in FIG. 24. The sliding movement causesthe pressing member 323 to rotate about a boundary angled portion 339defined between the horizontal portion 325 at the bottom of the pressingmember 323 and the right-hand slope 327a in the direction of the slope335 of the step 337. That is, the pressing member 323 rotatesrightwardly. As a result, the projecting piece 329 of the pressingmember 323 is disengaged from the upper end of the pressing section 321,so that the pressing section 321 is allowed to move upwardly. Thus, theswitching mechanism 309 according to this embodiment constitutes thereleasing means of the present invention.

[0231] When the operative members 43 a, 43 b are released from thepressure from the pressing section 321, the first ends 39 a, 39 b of theoperative members 43 a, 43 b are rotated as urged upwardly by thehelical springs 45 a, 45 b, as shown in FIG. 25. Because of the rotationof the first ends 39 a, 39 b of the operative members 43 a, 43 b, thedownward urging force on the first ends of the movable terminals 31 a,31 b is changed to the upward urging force, which upwardly rotates thefirst ends of the movable terminals 31 a, 31 b. Hence, the movableterminals 31 a, 31 b in contact with the normally open stationaryterminals 35 a, 35 b are separated therefrom to come into contact withthe normally close stationary terminals 33 a, 33 b. Thus, thepush-button switch 201 is shifted from the ON state to the second OFFstate.

[0232] At this time, the normally close contact (not shown) in theaccommodating portion 315 is opened. Therefore, whether the push-buttonswitch 301 is in the first OFF state or in the second OFF state can bedetermined by monitoring the open/close state of the normally closecontact.

[0233] According to the fifth embodiment, the equal effect to that ofthe first embodiment is naturally achieved. Furthermore, the fifthembodiment accomplishes the cost reduction of the push-button switch 301because the switching mechanism 309 has a simple configuration includingthe pressing section 321 and the pressing member 323.

[0234] (Sixth Embodiment)

[0235] Now referring to FIGS. 26 to 30, description will be made on asixth embodiment wherein the push-button switch of the present inventionis applied to a teaching pendant as an operation device for anindustrial manipulating robot. FIG. 26 is a front view of the teachingpendant of this embodiment, whereas FIG. 27 is a perspective viewthereof as seen from the rear side. FIGS. 28 to 30 are circuit diagramsof a push-button switch disposed in the teaching pendant.

[0236] A teaching pendant 401 as the operation device for the industrialmanipulating robot is a portable unit to be connected to a controldevice of the robot and has a configuration as shown in FIG. 26, forexample.

[0237] As seen in FIG. 26, the teaching pendant 401 is arranged suchthat opposite end portions of a pendant body 403 define grip portions405 a, 405 b to be held by hands. Disposed at a center of the pendantbody 403 is a liquid crystal display 407 (hereinafter referred to as“LCD”). As viewing a screen of this LCD 407, the operator properlymanipulates, with his thumbs or the like, a plural number of operationkeys 409 a, 409 b and others arranged on the opposite sides of the LCD407 of the pendant body 403 thereby teaching data such as a program tothe robot or operating the robot.

[0238] In this case, the robot cannot be taught by merely manipulatingthe operation keys 409 a, 409 b. It is designed such that the teachingof the program to the robot or the operation of the robot is noteffected unless the operation key 409 a, 409 b is manipulated after thepush-button switch is shifted to the ON state by manipulating anoperation section 411 a, 411 b of the push-button switch, the operationsections 411 a, 411 b disposed on back sides of the grip portions 405 a,405 b of the pendant body 403, as shown in FIG. 27.

[0239] The operation section 411 a, 411 b has an L-shaped section and isdesigned to be depressed by fingers of the right or left hand holdingthe pendant body 403. The operation sections 411 a, 411 b each containtherein a left-hand or right-hand push-button switch (not shown)according to the first embodiment. The push buttons of the left-hand andthe right-hand push-button switches can be depressed by depressing theoperation sections 411 a, 411 b, thereby turning ON or OFF thepush-button switch.

[0240] Next, an exemplary circuit connection of the above teachingpendant will be described with reference to FIG. 28.

[0241] As shown in FIG. 28, the teaching pendant comprises two circuitsformed by a first and a second circuit. In the first circuit, ac-contact RI of the right-hand push-button switch and a c-contact L1 ofthe left-hand push-button switch are connected in parallel. In thesecond circuit, the other c-contact R2 of the right-hand push-buttonswitch and the other c-contact L2 of the left-hand push-button switchare connected in parallel, whereas a normally close contact R3 of theright-hand push-button switch and a normally close contact L3 of theleft-hand push-button switch are connected in series with this parallelcircuit.

[0242] Such circuit connections permit the date entry via the teachingpendant 401 which is enabled by manually operating the teaching pendantwith either one of the left and the right hands for bringing the firstand the second circuits into conduction.

[0243] The right-hand and the left-hand push-button switches employ anyone of the push-button switches of the first to fourth embodimentsdescribed above. It is noted that NC1-R and NC2-R represent the normallyclose stationary terminals 33 a, 33 b of the c-contacts R1, R2 (the sameas the c-contacts 9 a, 9 b shown in FIG. 1, for example) constitutingthe right-hand push-button switch; that NO1-R, NO2-R represent thenormally open stationary terminals 35 a, 35 b of the c-contacts 9 a, 9 bconstituting the right-hand push-button switch; and that C1-R and C2-Rrepresent the movable terminals 31 a, 31 b of the c-contacts R1, R2constituting the right-hand push-button switch.

[0244] Likewise, NC1-L, NC2-L represent the normally close stationaryterminals 33 a, 33 b of the c-contacts L1, L2 (the same as thec-contacts 9 a, 9 b shown in FIG. 1, for example) constituting theleft-hand push-button switch; NO1-L, NO2-L represent the normally openstationary terminals 35 a, 35 b of the c-contacts L1, L2 76;constituting the left-hand push-button switch; and C1-L and C2-Lrepresent the movable terminals 31 a, 31 b of the c-contacts L1, L2constituting the left-hand push-button switch. On the other hand, R3 andL3 represent the normally close contacts constituting the right-hand andthe left-hand push-button switches, respectively.

[0245] Next, the operations of the teaching pendant according to thisembodiment will be described with reference to FIGS. 28 to 30. In astate where the operation sections 411 a, 411 b are undepressed as shownin FIG. 28, depressing the operation section 411 b with right hand, forexample, will close the two c-contacts R1, R2 of the right-handpush-button switch at a time, as shown in FIG. 29. This shifts theright-hand push-button switch from the first OFF state to the ON statewherein the first and the second circuits are brought into conduction.

[0246] This shifts the teaching pendant 401 to a teaching mode whereinthe teaching of the program to the robot is enabled. The teachingpendant 401 is adapted to be placed in the teaching mode by manipulatingthe pendant with either of the right and the left hands. Therefore, ifthe right hand is fatigued by depressing the operation section 411 b inorder to teach the program, for example, the teaching pendant 401 may bemaintained in the teaching mode by holding the pendant body 403 in theleft hand in turn and depressing the operation section 411 a with theleft hand.

[0247] When the right-hand operation section 411 b depressed to maintainthe right-hand push-button switch in the ON state is further depressed,both the c-contacts R1, R2 are shifted to the second OFF state while thenormally close contact R3 is turned OFF, as shown in FIG. 30. Hence, theright-hand push-button switch is shifted to the second OFF state. Thus,both the first and the second circuits are shut down so that theteaching pendant 401 is disabled for teaching of the program.

[0248] At this time, an effort to shift the left-hand push-button switchto the ON state by manipulating the left-hand operation section 411acannot bring the second circuit into conduction, because the normallyclose contacts R3, L3 of the right-hand and the left-hand push-buttonswitches are connected in series in the second circuit. That is, theoperation of the left-hand push-button switch is ineffective. Theteaching pendant 401 in this state may be placed again in the teachingmode by temporarily releasing the right hand from the operation section411 b to return the right-hand push-button switch to the first OFFstate.

[0249] According to the sixth embodiment, the pendant body 403 isprovided with the right-hand and the left-hand push-button switcheswherein one c-contacts R1, L1 and the other c-contacts R2, L2 areconnected in parallel, respectively. Therefore, the teaching pendant canbe If placed in the teaching mode by manually turning ON either one ofthe right-hand and the left-hand push-button switches.

[0250] Hence, if the right hand is fatigued by manipulating thepush-button switch, the operator may hold the pendant in his left handso as to continue to teach the program. The teaching pendant providesfor an efficient teaching operation with reduced load on the operatormanipulating the pendant for long hours.

[0251] Since the right-hand and the left-hand push-button switches havetheir normally close contacts connected in series, the second circuit isshut down when either one of the push-button switches is in the secondOFF state, for example. Therefore, the teaching pendant is preventedfrom being shifted to the teaching mode by manipulating the otherpush-button switch. As a result, the teaching of the program in thesecond OFF state during emergency can be avoided.

[0252] In the sixth embodiment described above, the circuit connectionsof the right-hand and the left-hand push-button switches via thec-contacts may be made the same way as those shown in FIG. 10illustrating the first embodiment. That is, the first and the secondcircuits are adapted to have the opposite ON/OFF positions relative toeach other. Needless to say, the equal effect to that of the foregoingembodiments can be attained in this case.

[0253] (Seventh Embodiment)

[0254] Now referring to FIGS. 31 and 32, description will be made on aseventh embodiment wherein the push-button switch of the presentinvention is applied to a teaching pendant as an operation device for anindustrial manipulating robot. FIG. 31 is a rear view of the teachingpendant according to this embodiment, whereas FIG. 32 is a group ofdiagrams for explaining the operations of the teaching pendant.

[0255] As shown in FIG. 31, a teaching pendant 501 according to thisembodiment is provided with a cover member 503 on a rear side thereof; asingle push-button switch 1 of the first embodiment covered by the covermember 503; and a left-hand and a right-hand manipulation levers 505 a,505 b for operative depression of the push-button switch 1.

[0256] The push-button switch 1 is disposed centrally of the rear sideof a pendant body 507 as covered by the cover member 503. Themanipulation lever 505 a, 505 b is laterally movable and formed with aplurality of laterally protruding projections 509 a, 509 b on one end Athereof, the projections arranged at regular space intervals in acomb-like fashion. These two manipulation levers 505 a, 505 b opposeeach other with their projections 509 a, 509 b interdigitated. Themanipulation lever 505 a, 505 b is formed with a grip portion 511 a, 511b on the other end thereof to be held by the right or left hand.

[0257]FIG. 32(a) is a sectional view taken on the line A-A in FIG. 31.As seen in FIG. 32(a), the projection 509 a, 509 b of the manipulationlever 505 a, 505 b is integrally formed with a locking piece 515 a, 515b at its distal end, the locking piece having a slope 513 a, 513 b andprotruded inwardly of the pendant body 507. A horizontal movement of themanipulation lever 505 a, 505 b brings the locking piece 515 a, 515 binto abutment against the push button 5 shaped like an arch in section,thereby depressing the push button 5.

[0258] Next, the operations of the teaching pendant of this embodimentwill be described with reference to FIG. 32. When, for example, themanipulation lever 505 a is moved by the left hand in a direction X inFIG. 32(a) in the first OFF state with the manipulation levers 505 a,505 b unmanipulated as shown in FIG. 32(a), the locking piece 515 a ofthe left-hand manipulation lever 505 a slides on the push button 5 todepress the push button, as shown in FIG. 32(b).

[0259] Thus, the push-button switch 1 is shifted to the ON state wherethe teaching pendant 501 enables the teaching of the program or thelike. In this state, the push button 5 can be depressed by means of theright-hand manipulation lever 505 b, as well. Accordingly, even if theleft hand is fatigued during the operation, the data entry may becontinued by holding the pendant by the right hand.

[0260] When the left-hand manipulation lever 505 a is further pulled inthe direction X in the ON state shown in FIG. 32(b), the locking piece515 a of the left-hand manipulation lever 505 a runs aground the pushbutton 5 as depressing the push button 5, as shown in FIG. 32(c). Thus,the push-button switch 1 is shifted to the second OFF state.

[0261] As a result, the teaching pendant 501 is disabled for teaching ofthe program or the like. At this time, the push button 5 is fullydepressed by the left-hand manipulation lever 505 a, as shown in FIG.32(c), so that the locking piece 515 b of the right-hand manipulationlever 505 b is unable to depress the push button 5. The teaching pendant501 in this state can be shifted to the teaching mode by the steps ofreturning the manipulation levers 505 a, 505 b to the initial positionsas shown in FIG. 32(a) and then turning ON the push-button switch 1 bymanipulating either one of the manipulation levers 505 a, 505 b.

[0262] According to the seventh embodiment, the equal effect to that ofthe sixth embodiment is naturally achieved. Furthermore, the teachingpendant features a simple circuit configuration because there isprovided only one push-button switch 1. Hence, the teaching pendantaccomplishes the cost reduction.

[0263] The provision of only one push-button switch 1 offers thefollowing merit. Once the push-button switch 1 is shifted to the secondOFF state, the teaching pendant is disabled for the teaching operationunless both the manipulation levers 505 a, 505 b are returned to theinitial positions thereby returning the push-button switch 1 to thefirst OFF state. This leads to an enhanced safety during the teachingoperation.

[0264] According to the seventh embodiment described above, thepush-button switch 1 is adapted to be depressed by the locking piece 515a, 515 b of the manipulation lever 505 a, 505 b slidably moved on thepush button 5. However, the present invention is not limited to thisarrangement and a modification may be made as shown in FIG. 33, forexample.

[0265] As shown in FIG. 33, an alternative arrangement may be made suchthat an intermediary member 517 is interposed between the locking pieces515 a, 515 b and the push button 5 in a manner to be movable in thedirection of depression of the push button 5, and that the push button 5id covered with a rubber cover 519.

[0266] According to this arrangement, manipulating the manipulationlever 505 a, 505 b causes the locking piece 515 a, 515 b to slide on theintermediary member 517 as moving the intermediary member 517 toward thependant body 507. This causes the intermediary member 517 to depress thepush button 5 via the rubber cover 519 thereby turning ON/OFF thepush-button switch 1.

[0267] Since the locking member 515 a 515 b is adapted to depress thepush button 5 via the intermediary member 517 and the rubber cover 519,the push button 5 is prevented from being deformed or broken by thesliding contact with the locking piece 515 a, 515 b. The rubber cover519 also serves as waterproof means. However, a similar effect can beobtained by an arrangement wherein the rubber cover 519 is dispensedwith and only the intermediary member 517 is provided for depressing thepush button 5.

[0268] Incidentally, the push-button switch 1 of the seventh embodimentmay be replaced by any one of the push-button switches of the second tofifth embodiments.

[0269] As a matter of course, the push-button switches of the second tofifth embodiments may each be provided with three or more c-contacts.

[0270] As a matter of course, the push-button switches of the first, thesecond, the fourth and the fifth embodiments may each be provided withthe external button such as illustrated by the third embodiment.

[0271] In the push-button switches of the foregoing embodiments, thepush button portion may be replaceable.

[0272] It is preferred that the push-button switches of the foregoingembodiments are provided with the waterproof configuration which may beconstituted by the rubber cover such as illustrated by the thirdembodiment or by a packing interposed in the push button portion.

[0273] It is to be noted that the present invention is not limited tothe foregoing embodiments and other various changes and modificationsmay be made thereto within the spirit and scope of the presentinvention.

[0274] Industrial Applicability

[0275] As mentioned supra, the push-button switch according to thepresent invention is provided with two or more contacts in the case forswitching ON/OFF the push-button switch, the contacts adapted to beturned ON/OFF at a time by depressing a single push button. In the eventof a failure of one of the contacts, for example, the push-button switchcan be switched ON/OFF by way of the other contacts. Thus, thepush-button switch is enhanced in reliability.

[0276] Since the contact has a so-called snap action configuration, aproper tactile click-touch or click sound is produced at the transitionof the push-button switch from the first OFF state to the ON state orfrom the ON state to the second OFF state. This assists the operatordepressing the push button 5 in determining whether or not thepush-button switch 1 is in the ON state enabling the data entry. Thus, apush-button switch featuring a good reliability is provided.

[0277] The teaching pendant of the present invention is arranged suchthat while one of the push-button switches is in the second OFF state,the operation of the other push-button switch via the other operationsection is disabled. Therefore, the data entry operation is not effectedif, for example, an operation is made to turn ON the other push-buttonswitch.

What is claimed is:
 1. A push-button switch designed to be switched OFF-ON-OFF by depressing a button comprising: a switch case; a push button depressibly supported by said switch case; a contact comprising a movable terminal disposed in said switch case in a manner that a first end thereof is rotatable about a second end thereof, and a normally open stationary terminal fixed to place in said switch case and arranged to be in or out of contact with said movable terminal through rotation of the first end of said movable terminal; an operative member disposed in said switch case in a manner that a first end thereof is rotatable as interlocked with depression of said push button; urging means having its opposite ends locked to the first end of said movable terminal and the first end of said operative member for urging the first end of said movable terminal while urging the first end of said operative member in a first direction; and releasing means brought into action by more than a predetermined amount of depression of said push button to release said operative member from interlocked relation with said push button, wherein when in conjunction with increase of an amount of depression of said push button, an amount of rotation of the first end of said operative member against said urging means is increased to a first dead point at which an urging force applied by said urging means to said movable terminal is changed from the first direction to a second direction, said movable terminal is brought into contact with said normally open stationary terminal thereby shifting said contact from a first OFF state to an ON state, wherein when the amount of rotation of the first end of said operative member released from the rotation against said urging means reaches a second dead point at which the urging force applied by said urging means to said movable terminal is changed from the second direction to the first direction, said movable terminal is moved away from said normally open stationary terminal thereby shifting said contact from said ON state to a second OFF state, and wherein two or more of said contacts are disposed in said switch case and are simultaneously turned ON or OFF by depressing said push button.
 2. The push-button switch as claimed in claim 1, wherein as to transition from said ON state to said first OFF state resulting from eased depression of said push button, the amount of rotation of the first end of said operative member to reach said second dead point is set smaller than the amount of rotation of the first end of said operative member to reach said first dead point.
 3. The push-button switch as claimed in claim 1 or 2, wherein one of said contacts includes a normally close stationary terminal, and wherein the one contact maintains said movable terminal and said normally close stationary terminal thereof in contacted relation when the other contacts are in said first OFF state, maintaining said movable terminal and said normally close stationary terminal thereof in separated relation when the other contacts are in said ON state, maintaining said movable terminal and said normally close stationary terminal thereof in contacted relation when the other contacts are in said second OFF state.
 4. The push-button switch as claimed in any one of claims 1 to 3, wherein an auxiliary contact is disposed in said switch case, said auxiliary contact designed to be opened or closed when said contacts are in said first OFF state and to be closed or opened when said contacts are in said second OFF state.
 5. The push-button switch as claimed in claim 4, wherein said auxiliary contact is provided in correspondence to each of said contacts.
 6. The push-button switch as claimed in claim 4 or 5, wherein said auxiliary contact comprises a normally close contact designed to be closed when said contacts are in said first OFF state and to be opened when said contacts are in said second OFF state, and is provided with forcible separation means for forcibly opening said auxiliary contact in said second OFF state.
 7. The push-button switch as claimed in any one of claims 1 to 6, comprising a distribution member for evenly distributing a pressing load applied by depressing said push button.
 8. The push-button switch as claimed in any one of claims 1 to 7, comprising a rubber cover mounted to place in a manner to cover said push button.
 9. The push-button switch as claimed in any one of claims 1 to 7, comprising an external button mounted to place in a manner to cover said push button.
 10. A teaching pendant including the push-button switch as claimed in any one of claims 1 to 9, wherein a pendant body includes a left-hand and a right-hand operation sections to be held in a left hand and a right hand, respectively, each of said operation sections including said push-button switch at an inner side thereof to be operated by gripping, and wherein gripping either one of said operation sections shifts said push-button switch therein to said ON state thereby enabling a data input operation.
 11. The teaching pendant as claimed in claim 10, wherein when either one of said operation sections is gripped to shift said push-button switch therein to said second OFF state, the gripping of the other operation section does not enable an operation of said push-button switch therein.
 12. A teaching pendant including the push-button switch as claimed in any one of claims 1 to 9, wherein a pendant body is provided with one piece of said push-button switch and a right-hand and a left-hand manipulation levers to be gripped by a right hand and a left hand, respectively, for operative depression of said push-button switch, and wherein either one of said manipulation levers is manipulated to shift said push-button switch to said ON state thereby enabling a data input operation.
 13. The teaching pendant as claimed in claim 12, wherein when either one of said manipulation levers is gripped to shift said push-button switch to said second OFF state, the gripping of the other manipulation lever does not enable an operation of said push-button switch. 